@article{GEArtic09,
  author = {Gregor Engels},
  title = {Guest Editorial to the Special Section on MODELS 2007},
  journal = {Software & Systems Modeling},
  year = {2010},
  volume = {9},
  number = {1},
  pages = {pp. 5--6},
  month = {Januar}
}

@article{EGGRR09,
  author = {Gregor Engels AND Michael Goedicke AND Ursula Goltz AND Andreas Rausch AND Ralf H. Reussner},
  title = {Design for Future – Legacy-Probleme von morgen vermeidbar?},
  journal = {Informatik-Spektrum},
  year = {2009},
  volume = {32},
  number = {5},
  pages = {393--397},
  month = {Oktober}
}

@article{egs08,
  author = {Baris G{\"u}ldali AND Stefan Sauer AND Gregor Engels},
  title = {Formalisierung der funktionalen Anforderungen mit visuellen Kontrakten und deren Einsatz f{\"u}r modellbasiertes Testen},
  journal = {Softwaretechnik-Trends},
  year = {2008},
  volume = {28},
  number = {3},
  pages = {12-16},
  month = {August},
  abstract = {Wir haben in diesem Beitrag einen Ansatz zurFormalisierung der UML-Anwendungsfallsbeschreibungenvorgestellt, um Anwendungsf{\"a}lleeffektiv f{\"u}r Testzwecke einsetzen zu k{\"o}nnen.Dabei werden die textuellen Beschreibungen derVor- und Nachbedingungen mit visuellen Kontraktenformalisiert. Die visuellen Kontrakte beschreibendie {\"A}nderungen bez{\"u}glich der fachlichenDaten nach der Ausf{\"u}hrung des Anwendungsfalls.Mit visuellen Kontrakten k{\"o}nnenw{\"a}hrend der Testfallspezifikation Testeingabengeneriert und w{\"a}hrend der Testausf{\"u}hrung Testausgaben{\"u}berpr{\"u}ft werden. F{\"u}r visuelle Kontraktewurden Werkzeuge entwickelt, die dieEinbindung der visuellen Kontrakte in den Entwicklungs-und Testprozess erm{\"o}glichen.}
}

@article{EngVo08,
  author = {Gregor Engels AND Markus Voß},
  title = {Quasar Enterprise},
  journal = {Informatik-Spektrum},
  year = {2008},
  volume = {31},
  number = {6},
  pages = {548--555},
  abstract = {Die Gestaltung und Weiterentwicklung großer Anwendungslandschaften gilt heutzutage als eine der gr{\"o}ßten Herausforderungen in der Softwaretechnik. Als L{\"o}sungsansatz wurde in den letzten Jahren vielfach das Paradigma einer serviceorientierten Architektur (SOA) diskutiert und insbesondere durch herstellerspezifische Technologien unterst{\"u}tzt. Dieser Beitrag widmet sich einer h{\"a}ufig vernachl{\"a}ssigten methodischen Herangehensweise und stellt mit Quasar Enterprise einen strukturierten und in der Praxis erprobten L{\"o}sungsansatz vor. Insbesondere werden konkrete Verfahrensbausteine f{\"u}r eine durchg{\"a}ngige Methode vorgestellt, die einem Architekten helfen, eine auf das zu unterst{\"u}tzende Gesch{\"a}ft ausgerichtete Anwendungslandschaft zu entwickeln und zu warten. Wesentliche Charakteristika von Quasar Enterprise sind der konsequente Einsatz einer serviceorientierten Herangehensweise, die Verwendung eines Architektur-Frameworks als Strukturierungsgrundlage und die Aufbereitung der Methode in Form von 20 Verfahrensbausteinen.}
}

@article{ESS2008,
  author = {Gregor Engels AND Stefan Sauer AND Christian Soltenborn},
  title = {Unternehmensweit verstehen – unternehmensweit entwickeln: Von der Modellierungssprache zur Softwareentwicklungsmethode},
  journal = {Informatik-Spektrum},
  year = {2008},
  volume = {31},
  number = {5},
  pages = {451--459},
  month = {October},
  abstract = {Sollen wir UML 1.4, UML 2.0 oder eine ganz andere Modellierungssprache f{\"u}r unsere Softwareentwicklung einsetzen? Der folgende Beitrag zeigt, dass bei der Festlegung einer unternehmensweiten Entwicklungsmethode nicht die Frage nach der Modellierungssprache im Vordergrund stehen sollte. Viel entscheidender f{\"u}r den Erfolg von Softwareentwicklungsprojekten in einem Unternehmen ist ein einheitliches Verst{\"a}ndnis der Entwicklungskonzepte und -artefakte sowie ihrer Beziehungen untereinander. Eine Einigung {\"u}ber ein unternehmensweites Dom{\"a}nenmodell der Softwareentwicklungskonzepte sollte deshalb vor der Auswahl von Modellierungssprachen, eines konkreten Vorgehensmodells und geeigneter Werkzeuge erfolgen.}
}

@article{Bals07,
  author = {Jan-Christopher Bals AND Fabian Christ AND Gregor Engels AND Martin Erwig},
  title = {ClassSheets - model-based, object-oriented design of spreadsheet applications},
  journal = {Journal of Object Technology, Special Issue: TOOLS EUROPE 2007},
  year = {2007},
  volume = {6},
  number = {9},
  pages = {383--398},
  month = {October },
  abstract = {Using spreadsheets is the preferred method to calculate, display or store anything that fits into a table-like structure. They are often used by end users to create applications. But they have one critical drawback - they are very error-prone.To reduce the error-proneness, we purpose a new way of object-oriented modeling of spreadsheets prior to using them. These spreadsheet models, termed ClassSheets, are used to generate concrete spreadsheets on the instance level.By this approach sources of errors are reduced and spreadsheet applications are easier to understand. }
}

@article{Bals2007,
  author = {Jan-Christopher Bals AND Fabian Christ AND Gregor Engels AND Stefan Sauer},
  title = {Software-Qualit{\"a}t - {\"u}berall! - Excel-lente Software},
  journal = {Forschungsforum Paderborn},
  year = {2007},
  volume = {10},
  pages = {56--60},
  month = {January}
}

@article{Doberkat2005,
  author = {Ernst-Erich Doberkat AND Gregor Engels AND Jan Hendrik Hausmann AND Marc Lohmann AND J{\"o}rg Pleumann AND Jens Schr{\"o}der},
  title = {Software Engineering and eLearning: The MuSofT Project},
  journal = {e-learning and education (eleed) Journal},
  year = {2005},
  volume = {2},
  month = {Dezember},
  abstract = {eLearning supports the education in certain disciplines. Here, we report about novel eLearning concepts, techniques, and tools to support education in Software Engineering, a subdiscipline of computer science. We call this "Software Engineering eLearning". On the other side, software support is a substantial prerequisite for eLearning in any discipline. Thus, Software Engineering techniques have to be applied to develop and maintain those software systems. We call this "eLearning Software Engineering". Both aspects have been investigated in a large joint, BMBF-funded research project, termed MuSofT (Multimedia in Software Engineering). The main results are summarized in this paper.}
}

@article{Engels2003a,
  author = {Gregor Engels AND Jan Hendrik Hausmann AND Marc Lohmann},
  title = {eLearning-Plattformen f{\"u}r die Hochschule: Bedarfsgerechte Bestimmung der Anforderungen},
  journal = {ForschungsForum Paderborn},
  year = {2003},
  volume = {6},
  pages = {44--47},
  month = {January},
  abstract = {Der Einfluss neuer Technologien auf die Art wie wir Lehren und Lernen wird seit einigen Jahren unter dem Begriff eLearning diskutiert. Auch an den Hochschulen gibt es Bemhungen, eLearning-Konzepte zu etablieren. Dabei versprechen so genannte eLearning-Plattformen ein integriertes und reibungsloses Zusammenarbeiten aller Beteiligten am eLearning zu ermglichen. Der Einsatz einer so zentralen Software in einem System wie der Hochschule ist ein komplexes Problem, fr dessen Bewltigung die Softwaretechnik, ein Fachgebiet der Informatik, Methoden und Sprachen bereitstellt. Zentrale Idee dabei ist es, von existierenden Strukturen und den Bedrfnissen der Anwender auszugehen. In diesem Beitrag wird beschrieben, wie die Analyse von Hochschulstrukturen und Prozessen der Planung des Einsatzes von eLearning-Plattformen dient.}
}

@article{EngelsKG2002c,
  author = {Gregor Engels AND Jochen K{\"u}ster AND Luuk Groenewegen},
  title = {Consistent Interaction of Software Components},
  journal = {Transactions of the SDPS: Journal of Integrated Design & Process Science},
  year = {2002},
  volume = {6},
  number = {4},
  pages = {2--22},
  month = {December},
  abstract = {Constructing complex software systems by integrating different software components isa promising and challenging approach. With the functionality of software components given by models it is possible to ensure consistency of such models before implementation in order to successfully build the system. Models consisting of different submodels, the absence of an overall formal semantics and the numerous possibilities of employing models requires the development of techniques ensuring the consistency. In this paper, we discuss the issue of consistency of models made up of different submodels proposing a concept for the management of consistency. Consistency management relies on a consistency concept and a process for ensuring consistency of models. We introduce a consistency concept for software components modeled in the Unified Modeling Language (UML) and devise suitable consistency checks. On this basis, we propose a process how to locate and resolve inconsistencies, thus ensuring the consistency of models and by that the consistency of componentbased systems derived from those models.}
}

@article{Doberkat2002,
  author = {Ernst-Erich Doberkat AND Gregor Engels},
  title = {MuSofT - Multimedia in der Softwaretechnik},
  journal = {Informatik Forschung und Entwicklung},
  year = {2002},
  volume = {1},
  number = {17},
  pages = {41--44},
  month = {Februar},
  abstract = {Im BMBF-Verbundprojekt MuSofT werden multimediale Lehrmaterialienf{\"u}r die Lehre der Softwaretechnik entwickelt. Neben den inhaltliche Aspekten sind dieDistribution und die Lizenzierung der erstellten Lehrmaterialien wichtige Themakomplexe,um die Nachhaltigkeit des Projektes zu erh{\"o}hen. In diesem Papier stellen wirdie in MuSofT gew{\"a}hlten L{\"o}sungen einer Open-Content-Lizenz sowie eines Portalszur Distribution der entwickelten Materialien vor.}
}

@article{Engels2001,
  author = {Gregor Engels AND Jens Gaulke AND Stefan Sauer},
  title = {Modelle f{\"u}r automobile Software - Objektorientierte Modellierung von eingebetteten, interaktiven Softwaresystemen im Automobil},
  journal = {Forschungsforum Paderborn},
  year = {2001},
  volume = {4},
  pages = {24--29},
  month = {January},
  abstract = {Wie in allen technischen Ger{\"a}ten werden auch im Automobil immer mehr Funktionen durch Softwaresysteme realisiert bzw. gesteuert. Bei einer Entwicklung derartiger Softwaresysteme wird im Rahmen eines ingenieurm{\"a}ßigen Entwicklungsprozesses zun{\"a}chst ein Modell erstellt. Hierzu muss eine Modellierungssprache zur Verf{\"u}gung stehen, die den Modellierer ad{\"a}quat bei der Erstellung des Modells unterst{\"u}tzt und ein einheitliches Verst{\"a}ndnis des Modells erm{\"o}glicht. }
}

@article{HE00,
  author = {Gregor Engels AND Reiko Heckel},
  title = {Graph Transformation and Visual Modeling Techniques},
  journal = {Bulletin of the EATCS},
  year = {2000},
  number = {71},
  pages = {186--202},
  month = {June},
  abstract = {In order to provide semantic support for visual modeling techniques, new techniques have to be developed which help us to narrow the conceptual gap between graph-based visual modeling techniques like the UML and established methodologies of programming language semantics almost exclusively based on trees and terms. Concepts and results from the area of graph transformation can be used both as a basis for high-level rule-based visual languages, and as semantic domain for visual modeling techniques focusing on the structural and behavioral aspects of today's software systems. Moreover, graph transformation can provide the necessary technology in order to develop the graph-based counterparts of the denotational, operational, or algebraic semantics paradigms in the field of programming languages.In this paper, we substantiate these claims by examples of the use of graph transformation as visual modeling notion, semantic domain, and for the semantics of diagram languages.}
}

@article{Depke1999,
  author = {Ralph Depke AND Gregor Engels AND Katharina Mehner AND Stefan Sauer AND Annika Wagner},
  title = {Ein Vorgehensmodell f{\"u}r die Multimedia-Entwicklung mit Autorensystemen},
  journal = {Informatik Forschung und Entwicklung},
  year = {1999},
  volume = {14},
  number = {2},
  pages = {83--94},
  month = {June},
  abstract = {Multimedia-Anwendungen sind interaktive Softwaresysteme und verlangen als solche, mit softwaretechnischen Methoden erstellt zu werden. Sie werden heutzutage in der Regel mit Hilfe von Autorensystemen entwickelt, die eine Ad-hoc-Entwicklung auf Implementierungsniveau unterst{\"u}tzen. Hierdurch und wegen des Fehlens etablierter Vorgehensmodelle f{\"u}r die Multimedia-Softwareentwicklung reduziert sich der Multimedia-Entwicklungsprozeß auf die Implementierungsphase. Dies f{\"u}hrt zu den in der Softwaretechnik bekannten Problemen wie mangelnder Konzeption und fehlender Dokumentation. Wir stellen in diesem Beitrag ein Vorgehensmodell f{\"u}r die Entwicklung von Multimedia-Anwendungen vor, in dessen Mittelpunkt eine Analyse- und Entwurfsphase im Hinblick auf eine Implementierung der Multimedia-Anwendung mit einem Autorensystem stehen. Ausgehend von einem frameworkbasierten Analysemodell der Anwendung und einem Modell der Realisierungsm{\"o}glichkeiten mit einem konkreten Autorensystem wird systematisch ein Implementierungsmodell auf Instanzebene abgeleitet, das als Eingabe f{\"u}r das Autorensystem verwendet wird. Das postulierte Vorgehensmodell wird exemplarisch f{\"u}r das Autorensystem Director am Beispiel der Dom{\"a}ne multimedialer Lehr-/Lernanwendungen erl{\"a}utert.}
}

@article{Andries1999,
  author = {Marc Andries AND Gregor Engels AND Annegret Habel AND Berthold Hoffmann AND Hans-J{\"o}rg Kreowski AND Sabine Kuske AND Detlef Plump AND Andy Sch{\"u}rr AND Gabriele Taentzer},
  title = {Graph Transformation for Specification and Programming},
  journal = {Science of Computer Programming},
  year = {1999},
  volume = {34},
  number = {1},
  pages = {1--54},
  month = {April },
  abstract = {The framework of graph transformation combines the potentials and advantages of both, graphs and rules, to a single computational paradigm. In this paper we present some recent developments in applying graph transformations as a rule-based framework for the specification and development of systems, languages, and tools. After reviewing the basic features of graph transformation, we discuss a selection of applications, including the evaluation of functional expressions, the specification of an interactive graphical tool, an example specification of abstract data types, and the definition of a visual database query language. The case studies indicate the need for suitable structuring principles which are independent of a particular graph transformation approach. To this end, we present the concept of a transformation unit, which allows systematic and structured specifications and programming based on graph transformation.}
}

@article{EHTE97b,
  author = {Gregor Engels AND Reiko Heckel AND Gabriele Taentzer AND Hartmut Ehrig},
  title = {A Combined Reference Model- and View-Based Approach to System Specification},
  journal = {Int. Journal of Software and Knowledge Engeneering},
  year = {1997},
  volume = {7},
  number = {4},
  pages = {457--477},
  month = {December},
  abstract = {The idea of a combined reference model- and view-based specification approach has been proposed recently in the software engineering community. In this paper we present a specification technique based on graph transformations which supports such a development approach. The use of graphs and graph transformations allows to satisfy the general requirements of an intuitive understanding and the integration of static and dynamic aspects on a well-defined and sound semantical base. On this background, formal notions of view and view relation are developed and the behaviour of views is described by a loose semantics. View relations are shown to preserve the behaviour of views. Moreover, we define a construction for the automatic integration of views which assumes that the dependencies between different views are described by a reference model. The views and the reference model are kept consistent manually, which is the task of a model manager. In case of more than two views more general scenarios are developed and discussed. We are able to show that the automatic view integration is compatible with the loose semantics, i.e., the behaviour of the system model is exactly the integration of the behaviours of the views. All concepts and results are illustrated at the well-known example of a banking system.}
}

@article{Engels97a,
  author = {Gregor Engels AND Hans J{\"u}rgen Schneider},
  title = {Guest Editors' Introduction},
  journal = {International Journal on Software Engineering and Knowledge Engineering (IJSEKE)},
  year = {1997},
  volume = {7},
  number = {4},
  pages = {397--400},
  month = {December },
  note = {},
  abstract = {Guest Editors Introduction}
}

@article{Andries1996,
  author = {Marc Andries AND Gregor Engels},
  title = {A Hybrid Query Language for the Extended Entity Relationship Model},
  journal = {Journal of Visual Languages and Computing},
  year = {1996},
  volume = {7},
  number = {3},
  pages = {321--352},
  month = {September},
  abstract = {We present the hybrid query language HQL/EER for an Extended Entity-Relationship model. As its main characteristic, this language allows a user to usebothgraphical and textual elements in the formulation of one and the same query. We demonstrate the look-and-feel of this query language by means of examples, and show how syntax and semantics of this language are formally defined using programmed graph rewriting systems. Although we present the language in the context of the EER model, the concept of hybrid languages is applicable in the context of other database models as well. We illustrate this claim by discussing a prototype implementation of a Hybrid Query Tool based on an object-oriented approach, namely the Object Modeling Technique (OMT).}
}

@article{Loehr-Richter1994,
  author = {Perdita L{\"o}hr-Richter AND Gregor Engels},
  title = {Visuelles Spezifizieren von komplexen Aktionen auf Datenbankstrukturen},
  journal = {GI-Datenbank Rundbrief},
  year = {1994},
  volume = {13},
  pages = {33--35},
  month = {March}
}

@article{EngelsLNSS1992,
  author = {Gregor Engels AND Claus Lewerentz AND Manfred Nagl AND Wilhelm Sch{\"a}fer AND Andy Sch{\"u}rr},
  title = {Building Integrated Software Development Environments, Part I: Tool Specification},
  journal = {ACM Transactions on Software Engineering and Methodology (TOSEM)},
  year = {1992},
  volume = {1},
  number = {2},
  pages = {135--167},
  month = {April},
  abstract = {The conceptual modeling approach of the IPSEN (Integrated Project Support Environment) project for building highly integrated environments is based on using attributed graphs to model and implement arbitrary object structures, in particular all kinds of software documents and their relationships. A language based on graph grammars, called PROGRESS (Programmed Graph REwriting SyStems), and a suitable method for the application of this language, called graph grammar engineering, have been developed over the last ten years. This language and method are being extensively used for specifying the complex graph structures of internal document representations as well as for specifying the functionality of all tools (editors, browsers, analyzers, debuggers) working on these internal representations. This paper explains the language and the method for applying the language based on a pragmatic nontrivial example of a software production process and its corresponding documents. In particular, it is shown why and how a graph grammar-based strongly typed language is perfectly suitable to formally specify highly integrated software tools. In addition, it is shown that the implementation of these tools (i.e., an environment composed of these tools) is systematically being derived from the formal specifications.}
}

@article{Engels1992a,
  author = {Gregor Engels AND Martin Gogolla AND Uwe Hohenstein AND Klaus H{\"u}lsmann AND Perdita L{\"o}hr-Richter AND Gunter Saake AND Hans-Dietrich Ehrich},
  title = {Conceptual Modelling of Database Applications Using an Extended ER Model},
  journal = {Data & Knowledge Engineering},
  year = {1992},
  volume = {9},
  number = {2},
  pages = {157--204},
  month = {December},
  abstract = {In this paper, we motivate and present a data model for conceptual design of structural and behavioural aspects of databases. We follow an object centered design paradigm in the spirit of semantic data models. The specification of structural aspects is divided into modelling of object structures and modelling of data types used for describing object properties. The specification of object structures is based on an Extended Entity--Relationship (EER) model. The specification of behavioural aspects is divided into the modelling of admissible database state evolutions by means of temporal integrity constraints and the formulation of database (trans)actions. The central link for integrating these design components is a descriptive logic--based query language for the EER model. The logic part of this language is the basis for static constraints and descriptive action specifications by means of pre- and postconditions. A temporal extension of this logic is the specification language for temporal integrity constraints. We emphasize that the various aspects of a database application are specified using several appropriate, but yet compatible formalisms, which are integrated by a unifying common semantic.}
}

@article{Hohenstein1992,
  author = {Uwe Hohenstein AND Gregor Engels},
  title = {SQL/EER - Syntax and Semantics of an Entity-Relationship-Based Query Language},
  journal = {Information Systems},
  year = {1992},
  volume = {17},
  number = {3},
  pages = {209--242},
  abstract = {This paper presents the high-level query language SQL/EER for an extended Entity-Relationship model (EER model). SQL/EER directly supports all the concepts of the EER model and takes into account well-known features that are integral part of contemporary query languages, e.g. arithmetic and aggregate functions. In contrast to usual descriptions of query languages, we give SQL/EER a complete formal specification of syntax and sematics. This syntax is defined by using an attribute grammar which fixes the context-free structure and the context-sensitive rules. The operational semantics is defined by formally translating SQL/EER queries into queries of an existing, semantically well-defined calculus. The attribute grammar is extended to cover this translation, too.The query language SQL/EER is used in a database design environment. In this context, the formal specification of its syntax and the semantics has been used to implement a syntax-directed editor and a query interpreter for SQL/EER.}
}

@article{Engels1983,
  author = {Gregor Engels AND Udo Pletat AND Hans-Dietrich Ehrich},
  title = {An Operational Semantics for Specifications of Abstract Data Types with Error Handling},
  journal = {Acta Informatica},
  year = {1983},
  volume = {9},
  number = {3},
  pages = {235--254},
  abstract = {A new approach to an operational treatment of errors and exceptions in specifications of abstract data types is presented. Considering a specification as a term rewriting system, we define an operational semantics and give conditions that are sufficient for its well-definedness (Church-Rosser property). Also, we give conditions that are sufficient for the termination of reduction strategies, respecting the specified error and exception handling.}
}

@article{Engels1983a,
  author = {Gregor Engels AND Rupert Gall AND Manfred Nagl AND Wilhelm Sch{\"a}fer},
  title = {Software Specification Using Graph Grammars},
  journal = {Computing},
  year = {1983},
  volume = {31},
  number = {4},
  pages = {317--346},
  month = {December},
  abstract = {The following paper,demonstrates that programmed sequential graph grammars can be used in a systematic proceeding to specify tbe changes of high level intermediate data structures arising in a programming support environment, in which all tools work in an incremental and syntax-driven mode. In this paper we lay stress upon the way to get the specification rather than on the result of this process. Therefore, we give here some approach to "specification engineering" using graph grammars. This approach is influenced by the syntactical definition of the underlying language for Programming in the Small, the module concept etc. to be supported on one side but also by the idea of the user interface.}
}

@book{Engels2008,
  author = {Gregor Engels AND Andreas Hess AND Bernhard Humm AND Oliver Juwig AND Marc Lohmann AND Jan-Peter Richter AND Markus Voß AND Johannes Willkomm},
  title = {Quasar Enterprise: Anwendungslandschaften serviceorientiert gestalten},
  publisher = {dpunkt-Verlag},
  year = {2008},
  month = {M{\"a}rz},
  abstract = {IT-Anwendungslandschaften in Unternehmen sind komplexe {\"u}ber Jahre gewachsene Gebilde. Sie architektonisch zu gestalten und nachhaltig zu entwickeln braucht eine eigene Technologie jenseits der klassischen Softwaretechnik. Der Ansatz serviceorientierter Architekturen (SOA) ist ein wichtiges Instrument, reicht aber alleine nicht aus.In Quasar Enterprise haben Experten des Softwareunternehmens sd&m eine durchg{\"a}ngige Architekturmethodik f{\"u}r die serviceorientierte Gestaltung von Anwendungslandschaften zusammengetragen, die Erfahrungen aus Dutzenden von Beratungs-, Integrations- und großen Softwareprojekten widerspiegelt. Das Besondere an Quasar Enterprise ist die Sammlung sehr konkreter Methoden, Regeln, Referenzarchitekturen und Muster f{\"u}r die Gestaltung - ausgehend von der Architektur des Gesch{\"a}fts, {\"u}ber die logische Strukturierung der IT in Services und Dom{\"a}nen, bis hin zu physischen Komponenten und Schnittstellen inkl. deren Kopplung {\"u}ber technische Integrationsplattformen.Teil I beschreibt ein fiktives, aber realistisches Projekt aus der Sicht eines IT-Architekten. Der Leser schaut ihm bei seiner Arbeit {\"u}ber die Schulter und erlangt dabei ein intuitives Verst{\"a}ndnis der Artefakte und Verfahrensbausteine von Quasar Enterprise. Das Vorgehen im Projekt erlebt er dabei beispielhaft.Teil II vertieft das Erlernte systematisch. Die Grundlagen f{\"u}r Anwendungslandschaften und SOA werden eingef{\"u}hrt und dann Schritt f{\"u}r Schritt Begriffe, Zusammenh{\"a}nge und Vorgehensbausteine erl{\"a}utert. Die Beziehungen zwischen Architekturentscheidungen und Qualit{\"a}tszielen werden transparent gemacht und Verweise auf weiterf{\"u}hrende Literatur gegeben. Das Buch richtet sich an alle, die etwas {\"u}ber Anwendungslandschaften und SOA in der Praxis wissen wollen. Prim{\"a}re Zielgruppe sind IT-Architekten, erfahrene Softwareingenieure und Berater. }
}

@mastersthesis{Engels1980,
  author = {Gregor Engels AND Udo Pletat},
  title = {Analyse von Regelschemata f{\"u}r Unterbaum-Ersetzungssysteme},
  school = {Universit{\"a}t Dortmund, Abt. Informatik},
  year = {1980},
  month = {M{\"a}rz}
}

@incollection{oswuensc2010,
  author = {Sebastian Oster AND Andreas W{\"u}bbeke AND Gregor Engels AND Andy Sch{\"u}rr},
  title = {Model-Based Software Product Lines Testing Survey},
  booktitle = {Model-Based Testing For Embedded Systems},
  year = {2011},
  editor = {Pieter Mosterman, Ina Schieferdecker,Justyna Zander},
  publisher = {CRC Press},
  month = {Mai}
}

@incollection{Engels08-4,
  author = {Gregor Engels AND Andreas Hess AND Bernhard Humm AND Oliver Juwig AND Marc Lohmann AND Jan-Peter Richter AND Markus Voß AND Johannes Willkomm},
  title = {Anwendungslandschaften serviceorientiert gestalten},
  booktitle = {Handbuch der Softwarearchitektur},
  year = {2008},
  editor = {R. Reussner, W. Hasselbring},
  pages = {151--178},
  organization = {sd&m},
  publisher = {dpunkt-Verlag},
  month = {March},
  note = {2. Auflage},
  abstract = {Service-orientierte Architekturen (SOA) – wie mache ich das konkret? Wir stellen mit Quasar Enterprise einen durchg{\"a}ngigen, serviceorientierten Ansatz zur Gestaltung großer Anwendungslandschaften vor. Hierzu verwenden wir ein Architektur-Framework zur Strukturierung der methodischen Schritte und f{\"u}hren ein Dom{\"a}nenmodell zur Pr{\"a}zisierung der Begrifflichkeiten und Entwicklungsartefakte ein. Die dargestellten methodischen Bausteine und Richtlinien beruhen auf langj{\"a}hrigen Erfahrungen in der industriellen Softwareentwicklung bei der sd&m AG.}
}

@incollection{Eng08,
  author = {Gregor Engels},
  title = {Eintrag "Modellierungssprache"},
  booktitle = {Enzyklop{\"a}die der Wirtschaftsinformatik},
  year = {2008},
  editor = {K. Kurbel, J. Becker, N. Gronau, E. Sinz, L. Suhl},
  publisher = {Oldenbourg Wissenschaftsverlag},
  month = {October}
}

@incollection{Engels2006,
  author = {Gregor Engels AND Marc Lohmann AND Annika Wagner},
  title = {The Web Application Development Process},
  booktitle = {Web Engineering: The Discipline of Systematic Development of Web Applications},
  year = {2006},
  editor = {G. Kappel, B. Pr{\"o}ll, S. Reich, W. Retschitzegger},
  publisher = {Wiley},
  month = {May},
  abstract = {The current situation of ad hoc development of Web applications reminds us of the software development practices of the 1960s, before it was realized that the development of applications required more than programming expertise. This book counteracts this situation by giving a comprehensive, practice-oriented and thorough insight into the new discipline of Web Engineering.The text highlights the need to examine and re-use the body of knowledge found within software engineering. It demonstrates how to use that knowledge within the Web environment, in order to achieve a highly disciplined and methodological means of producing Web-based software, putting emphasize on current practices, experiences and pitfalls. The book demonstrates the distinctions between software engineering and Web engineering, for instance, the shorter lead times that Web engineering has compared to its software counterpart, whilst also demonstrating the rapid prototyping and agile methods of development needed to meet these criteria.The book covers important topics of Web Engineering, including requirements analysis, design, architectures, technologies, test, operation and maintenance; this is complemented by in-depth knowledge about Web project management and process issues as well as important quality aspects of Web applications like usability, performance and security. An overview of Semantic Web concepts points the way to the development of future Web applications. }
}

@incollection{Engels2005a,
  author = {Gregor Engels AND Reiko Heckel AND Alexey Cherchago},
  title = {Flexible Interconnection of Graph Transformation Modules - A Systematic Approach},
  booktitle = {Formal Methods in Software and System Modeling. Essays Dedicated to Hartmut Ehrig on the Occasion of His 60th Birthday},
  year = {2005},
  editor = {H.-J. Kreowski, U. Montanari, F. Orejas, G. Rozenberg, G. Taentzer},
  pages = {38--63},
  publisher = {Springer},
  abstract = {Modularization is a well-known concept to structure software systems as well as their specifications. Modules are equipped with export and import interfaces and thus can be connected with other modules requesting or providing certain features. In this paper, we study modules the interfaces of which consist of behavioral specifications given by typed graph transformation systems. We introduce a framework for classifying and systematically defining relations between typed graph transformation systems. The framework comprises a number of standard ingredients, like homomorphisms between type graphs and mappings between sets of graph transformation rules. The framework is applied to develop a novel concept of substitution morphism by separating preconditions and effects in the specification of rules. This substitution morphism is suited to define the semantic relation between export and import interfaces of requesting and providing modules.}
}

@incollection{Engels2005,
  author = {Gregor Engels AND Alexander F{\"o}rster AND Reiko Heckel AND Sebastian Th{\"o}ne},
  title = {Process Modeling using UML},
  booktitle = {Process-Aware Information Systems},
  year = {2005},
  editor = {M. Dumas, W. van der Aalst, A. ter Hofstede},
  pages = {85-117},
  publisher = {Wiley},
  abstract = {This chapter provides an introduction to the Unified Modeling Language (UML), a widely adopted object-oriented modeling standard, and shows how the language can be applied to (business) process modeling. As major perspectives of process modeling with UML 2.0, the chapter covers control flow, data objects and object flow, organizational structure, business partner interactions, and system-specific process models. Various types of UML diagrams are presented with a special focus on how these diagrams fit together and complement each other to form a coherent view of a process. Moreover, a running example is used throughout the chapter to illustrate the different facets of a process model.}
}

@incollection{Engels2003,
  author = {Gregor Engels AND Marc Lohmann AND Annika Wagner},
  title = {Entwicklungsprozess von Web-Anwendungen},
  booktitle = {Web Engineering: Systematische Entwicklung von Web-Anwendungen},
  year = {2003},
  editor = {G. Kappel, B. Proell, S. Reich, W. Retschnitzegger},
  pages = {239--264},
  publisher = {dpunkt-Verlag},
  month = {October},
  abstract = {Ist es m{\"o}glich klassische Softwareentwicklungsprozesse f{\"u}r die Entwicklung von Web-Anwendungen zu nutzen? Dazu formulieren wir sechs grundlegende Anforderungen an den Prozess der Entwicklung von Web-Anwendungen. Diese Anforderungen werden zur Evaluation des Rational Unified Process (RUP) und von Extreme Programming (XP) verwendet. Dabei konzentrieren wir uns auf den eigentlichen Prozess, d.h. die Organisation des Ablaufs der Entwicklung, und lassen die zugrunde liegenden Methoden so weit wie m{\"o}glich ausgeklammert. Es zeigt sich,dass keiner der Prozesse in der Lage ist, alle Anforderungen zu erf{\"u}llen. Die St{\"a}rken des RUP liegen in seiner Anpassbarkeit an den Grad der Komplexit{\"a}t der zu entwickelnden Anwendung. Die St{\"a}rken von XP dagegen liegen im Umgang mit kurzen Entwicklungszeiten und sich erst entwickelnden bzw. sich {\"a}ndernden Anforderungen.}
}

@incollection{Engels2002b,
  author = {Gregor Engels AND Ernst-Erich Doberkat},
  title = {Multimedia in der Informatik-Lehre},
  booktitle = {Informatik bewegt. 32. Jahrestagung der Gesellschaft f{\"u}r Informatik, 2002, Lecture Notes in Informatics},
  year = {2002},
  editor = {S. Schubert, B. Reusch, N. Jesse},
  pages = {377--384},
  publisher = {Gesellschaft f{\"u}r Informatik},
  month = {October},
  abstract = {Neue Medien werden in der universit{\"a}ren Lehre in zunehmendem Maßeeingesetzt. Nachdem sich noch vor einigen Jahren nur vereinzelte Pilotprojekte mitdem Thema besch{\"a}ftigt haben, wird inzwischen eine Vielzahl von Projekten {\"o}ffentlichgef{\"o}rdert. Als Beispiel sei das BMBF-F{\"o}rderprogramm Neue Medien inder Hochschullehre genannt.In der Informatik haben nicht zuletzt die hohen Studierendenzahlen dazu beigetragen,multimediale Elemente in der Lehre als ein m{\"o}gliches Mittel zur Bew{\"a}ltigungder hohen Lehrbelastung bei gleichzeitiger Wahrung von Qualit{\"a}t und Vielfalt derLehre anzusehen. Das fachliche Interesse vieler Informatiker am Thema Multimediakommt hinzu.Im Workshop Multimedia in der Informatik-Lehre wird ein {\"U}berblick {\"u}ber gegenw{\"a}rtigeAns{\"a}tze zur Unterst{\"u}tzung der Lehre in der Informatik mit multimedialenMitteln gegeben und es werden Erfahrungen und Konsequenzen diskutiert.}
}

@incollection{Engels2002a,
  author = {Gregor Engels AND Stefan Sauer},
  title = {Object-oriented Modeling of Multimedia Applications},
  booktitle = {Handbook of Software Engineering and Knowledge Engineering},
  year = {2002},
  editor = {S.K. Chang},
  pages = {21--53},
  publisher = {World Scientific Publishing Co. Pte. Ltd.},
  abstract = {The field of multimedia software engineering is still in an inmature state. Significant research and development has been dedicated towards multimedia services and systems technology such as networking or database systems. Multimedia document formats have been standardized. But when it comes to multimedia application development, the development process is truncated to an implement and test method. Either specialized multimedia authoring systems or multimedia frameworks or toolkits complementing programming languages or system software are directly used for implementation. No preceding modeling phases for requirements specification, analysis, or design of the system to build are enforced. The development of sophisticated multimedia process models and established, usable graphical notations tailored to the specification of multimedia systems is still underway.In order to fill this gap, it is the purpose of this chapter to show current achievements in object-oriented modeling of multimedia applications. Based on an analysis of the state of the art in multimedia application development, we shortly present approaches to object-oriented hypermedia modeling and extensions of the Unified Modeling Language (UML) for hypermedia and interactive systems. The main part of the chapter is dedicated towards a recent approach to the Object-oriented Modeling of MultiMedia Applications (OMMMA).}
}

@incollection{Engels2002,
  author = {Gregor Engels AND Luuk Groenewegen},
  title = {Towards Team-Automata-Driven Object-Oriented Collaborative Work},
  booktitle = {Formal and Natural Computing: Essays Dedicated to Grzegorz Rozenberg},
  year = {2002},
  editor = {W. Brauer, H. Ehring, J. Karhum{\"a}ki, A. Salomaa},
  pages = {257--276},
  publisher = {Springer},
  abstract = {The paper studies and compares two different approaches to model communication and cooperation. The approaches are team automata, a well-defined variant of communicating automata, and statecharts, heavily used in object-oriented modelling methods. The comparison yields interesting insights for modelling communication and cooperation. In particular, the differences between action-based, synchronous and state-based, asynchronous communication are elucidated.}
}

@incollection{EngelsGK2000,
  author = {Gregor Engels AND Luuk Groenewegen AND Gerti Kappel},
  title = {Coordinated Collaboration of Objects},
  booktitle = {Proceedings of Advances in Object-Oriented Modeling},
  year = {2000},
  editor = {M.P. Papazoglou, S. Spaccapietra, Z. Tari},
  pages = {307--332},
  publisher = {The MIT Press},
  abstract = {The computer has evolved from the purpose of pure number crunching to supporting the coordinated collaboration between human and/or artificial beings to reach a certain goal. Object-oriented modelling techniques based on the central notions of object interaction and object collaboration should provide the semantic expressivity to model such coordinated collaboration. Based on an investigation of the object-oriented modelling standard UML, however, the weaknesses of the existing modelling concepts are revealed. SOCCA is presented instead, which is an object-oriented specification language supporting the arbitrarily fine-grained synchronisation of processes, i.e., active objects. Based on several examples of the EU rental car system the expressive power of SOCCA is discussed and compared to related approaches.}
}

@incollection{Engels2000b,
  author = {Gregor Engels AND Ralph Depke AND Katharina Mehner},
  title = {Ergebnisse - vergleichende Darstellung},
  booktitle = {Multimedia in der wirtschaftswissenschaftlichen Lehre, Erfahrungsbericht},
  year = {2000},
  editor = {E.-E. Doberkat, G. Engels, M. Grauer, H.L. Grob, U. Kelter, W. Leidhold, V. Nienhaus},
  pages = {277--294},
  publisher = {LIT},
  month = {April},
  abstract = {Auf der Grundlage der im vorherigen Kapitel zusammengefaßten Beschreibungen derAktivit{\"a}ten an den einzelnen Standorten Bochum, K{\"o}ln, M{\"u}nster und Siegen soll in diesemKapitel versucht werden, die beschriebenen Erfahrungen zu strukturieren und zuvergleichen. Hierbei geht es in erster Linie um eine qualitative Analyse. Es wird also nichtgefragt und bewertet, welche konkret quantitativ meßbaren Ergebnisse erzielt wurden,sondern welcher Standort welche Aktivit{\"a}ten durchgef{\"u}hrt hat, um das gesteckte Ziel zuerreichen. Das Ziel dieser vergleichenden Analyse liegt vor allem in dem Erkenntnisgewinn,welche Aktivit{\"a}ten von welchen Personenkreisen in einer Fakult{\"a}t durchgef{\"u}hrt werdenk{\"o}nnen bzw. sollten, um eine ad{\"a}quate Unterst{\"u}tzung der Lehre durch Multimedia-Technikenzu erzielen.}
}

@incollection{Engels2000a,
  author = {Gregor Engels AND Udo Kelter AND Ralph Depke AND Katharina Mehner},
  title = {Unterst{\"u}tzende Angebote der Softwarebegleitgruppe},
  booktitle = {Multimedia in der wirtschaftswissenschaftlichen Lehre, Erfahrungsbericht},
  year = {2000},
  editor = {E.-E. Doberkat, G. Engels, M. Grauer, H.L. Grob, U. Kelter, W. Leidhold, V. Nienhaus},
  pages = {27--56},
  publisher = {LIT},
  month = {April},
  abstract = {In diesem Kapitel sollen das Vorgehensmodell zur Entwicklung von multimedialenLehreinheiten und der Fragebogen zur Erstellung eines deskriptiven Vorgehensmodellsvorgestellt werden. Diese Dokumente sind von der Softwarebegleitgruppe im Projektverlauff{\"u}r die Projektteilnehmer aus den wirtschaftswissenschaftlichen Fakult{\"a}ten erstellt worden.}
}

@incollection{Heckel1999,
  author = {Reiko Heckel AND Gregor Engels AND Hartmut Ehrig AND Gabriele Taentzer},
  title = {A View-based Approach to System Modeling Based on Open Graph Transformation Systems},
  booktitle = {Handbook of Graph Grammars and Computing by Graph Transformations, Volume 2: Applications, Languages and Tools},
  year = {1999},
  editor = {H. Ehrig, G. Engels, H.-J. Kreowski, G. Rozenberg},
  pages = {639--668},
  publisher = {World Scientific},
  abstract = {The idea of a combined reference model- and view-based specification approach has been proposed recently in the software engineering community. In this chapter we present a specification technique based on open graph transformation systems (in the double-pushout approach) by a new loose semantics for rule-based systems, which allows to model the interaction between different views, and by explicit frame conditions which restrict these interactions to an interface of open types. On this background, formal notions of view and view relation are developed and the behavior of views is described by the loose semantics. Based on the assumption that dependencies between different views are faithfully described by a common reference model, a construction is developed for the automatic integration of views. The views and the reference model are kept consistent manually, which is the task of a model manager. All concepts and results are illustrated at the well-known example of banking system.}
}

@incollection{Heckel1999a,
  author = {Reiko Heckel AND Gregor Engels AND Hartmut Ehrig AND Gabriele Taentzer},
  title = {Classification and Comparison of Module Concepts for Graph Transformation Systems},
  booktitle = {Handbook of Graph Grammars and Computing by Graph Transformations, Volume 2: Applications, Languages and Tools},
  year = {1999},
  editor = {H. Ehrig, G. Engels, H.-J. Kreowski, G. Rozenberg},
  pages = {669--689},
  publisher = {World Scientific},
  abstract = {In this chapter we use a three-level approach for analyzing module concepts forgraph transformation systems. Based on the observation that module architecturesconsist of basic specications like body or export interface and relations like theimplementation relation between them, or the import relation between a client anda server module, module concepts are characterized by answering the questions1. What are the basic specifications?2. Which relations between specifications are used?3. How are specifications and relations combined to module architectures?These three questions are investigated for five module concepts available in theliterature. As a reference example, a samplemodular specification of resource management in distributed operating systems is presented.}
}

@incollection{Andries1997,
  author = {Gregor Engels AND Jan Rekers AND Marc Andries},
  title = {How to represent a visual specification},
  booktitle = {Visual Language Theory},
  year = {1997},
  editor = {K. Marriott, B. Meyer},
  pages = {241--255},
  publisher = {Springer}
}

@incollection{Engels1996,
  author = {Gregor Engels AND Manfred Nagl AND Wilhelm Sch{\"a}fer AND Bernhard Westfechtel},
  title = {Tight Integration on One Document: The Programming Environment},
  booktitle = {Building Tightly Integrated Software Development Environments: The IPSEN Approach},
  year = {1996},
  editor = {M. Nagl},
  pages = {170--177},
  publisher = {Springer}
}

@incollection{Ebert1994,
  author = {J{\"u}rgen Ebert AND Gregor Engels},
  title = {Design Representation},
  booktitle = {Encyclopedia of Software Engineering},
  year = {1994},
  editor = {J.J. Marciniak},
  pages = {382-394},
  publisher = {John Wiley & Sons, Inc.},
  note = {New York,NY (USA)},
  abstract = {This article gives an overview on how to represent the outcome of the software design phase in design documents. The descriptive aspects of the design description languages are stressed. The focus is on sequential systems and the description is arranged according to the main paradigms that are used in indentifying software components. Following a general discussion on how to represent software architectures of large systems, each design paradigm is discussend separately with its basic concepts, its historical background and its main variants. Some multiparadigmatic approaches are discussed, as well which integrate several of the aspects introduced before.}
}

@incollection{Engels1994,
  author = {Gregor Engels AND Luuk Groenewegen},
  title = {SOCCA: Specifications of Coordinated and Cooperative Activities},
  booktitle = {Software Process Modelling and Technology},
  year = {1994},
  editor = {A. Finkelstein, J. Kramer, B.A. Nuseibeh},
  pages = {71--102},
  publisher = {Research Studies Press}
}

@incollection{Engels1989,
  author = {Gregor Engels AND Wilhelm Sch{\"a}fer},
  title = {Programmentwicklungsumgebungen: Konzepte und Realisierung},
  booktitle = {Leitfaeden der angewandten Informatik},
  year = {1989},
  publisher = {Teubner}
}

@inproceedings{bruSanEng2010_sqmb,
  author = {Frank Br{\"u}seke AND Yavuz Sancar AND Gregor Engels},
  title = {Architecture-Driven Derivation of Performance Metrics},
  booktitle = {Proceedings of Software-Qualit{\"a}tsmodellierung und -bewertung (SQMB '10), M{\"u}nchen, Germany},
  year = {2010 - to be published},
  editor = {Wagner, Stefan: Broy, Manfred; Deissenboeck, Florian ; M{\"u}nch, J{\"u}rgen; Liggesmeyer, Peter},
  publisher = {Technische Universit{\"a}t M{\"u}nchen}
}

@inproceedings{SQMB10TQ,
  author = {Yavuz Sancar AND Frank Br{\"u}seke AND Gregor Engels},
  title = {Teststufenspezifische Qualit{\"a}tsattribute f{\"u}r die Qualit{\"a}tsbewertung von nichtfunktionalen Anforderungen},
  booktitle = {Proceedings of Software-Qualit{\"a}tsmodellierung und -bewertung (SQMB '10), M{\"u}nchen, Germany},
  year = {2010 - to be published},
  editor = {Wagner, S.; Broy, M.; Deissenboeck, F. ; M{\"u}nch, J.; Liggesmeyer, P.}
}

@inproceedings{KuesterGE10,
  author = {Jochen K{\"u}ster AND Christian Gerth AND Gregor Engels},
  title = {Dynamic Computation of Change Operations in Version Management of Business Process Models},
  booktitle = {Proceedings of the 6th European Conference on Modelling Foundations and Applications (ECMFA'10)},
  year = {2010},
  editor = {T. K{\"u}hne, B. Selic},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  abstract = {Version management of business process models requires that changescan be resolved by applying change operations. In order to give a user maximalfreedom concerning the application order of change operations, position parametersof change operations must be computed dynamically during change resolution.In such an approach, change operations with computed position parametersmust be applicable on the model and dependencies and conflicts of changeoperations must be taken into account because otherwise invalid models can beconstructed. In this paper, we study the concept of partially specified change operationswhere parameters are computed dynamically. We provide a formalizationfor partially specified change operations using graph transformation and providea concept for their applicability. Based on this, we study potential dependenciesand conflicts of change operations and show how these can be taken into accountwithin change resolution. Using our approach, a user can resolve changes of businessprocess models without being unnecessarily restricted to a certain order.}
}

@inproceedings{Baumann2009,
  author = {Andrea Baumann AND Gregor Engels AND Alexander Hofmann AND Stefan Sauer AND Johannes Willkomm},
  title = {A Holistic Software Engineering Method for Service-Oriented Application Landscape Development},
  booktitle = {Proceedings of the First NAF Academy Working Conference on Practice-Driven Research on Enterprise Transformation (PRET 2009), Amsterdam (The Netherlands)},
  year = {2009},
  pages = {1--17},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  abstract = {Enterprises are transforming into enterprises which follow from a business as well as from an IT perspective a service-oriented paradigm. This change towards service-oriented enterprise and IT architectures has to be reflected in the methodologies of developing whole application landscapes as well as individual applications. Quasar (Quality Software Architecture) has been developed as the standard architecture and development method of Capgemini sd&m for individual applications. For the development of service-oriented enterprise application landscapes, Quasar Enterprise has been designed. Both Quasar and Quasar Enterprise are integrated with each other within a holistic software engineering method to seamlessly cover the full development lifecycle of service-oriented application landscapes, from business modeling and service design to actual software development. In this paper, we illustrate how a company-wide ontology of development artifacts serves as the key feature for integrating both methods.}
}

@inproceedings{ECMDA-09,
  author = {Jochen K{\"u}ster AND Christian Gerth AND Gregor Engels},
  title = {Dependent and Conflicting Change Operations of Process Models},
  booktitle = {Proceedings of the 5th European Conference on Model-Driven Architecture Foundations and Applications (ECMDA-FA'09)},
  year = {2009},
  pages = {158--173},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  abstract = {Version management of models is common for structural diagrams such as class diagrams but still challenging for behavioral models such as process models. For process models, conflicts of change operations are difficult to resolve because often dependencies to other change operations exist. As a consequence, conflicts and dependencies between change operations must be computed and shown to the user who can then take them into account while creating a consolidated version. In this paper, we introduce the concepts of dependencies and conflicts of change operations for process models and provide a method how to compute them. We then discuss different possibilities for resolving conflicts. Using our approach it is possible to enable version management of process models with minimal manual intervention of the user.}
}

@inproceedings{wuebb2009,
  author = {Martin Assmann AND Gregor Engels AND Thomas von der Maßen AND Andreas W{\"u}bbeke},
  title = {Identifying Software Product Line Component Services},
  booktitle = {Proceedings of International Conference on Evaluation of Novel Approaches to Software Engineering (ENASE 09)},
  year = {2009},
  editor = {Stefan Jablonski and Leszek Maciaszek},
  pages = {45–56},
  abstract = {Software Product Line (SPL) development provides the possibility of reusing common parts in similar software products. However the SPL approach does not centrally improve the maintenance of software products of a Software Product Line. This paper presents an approach for reducing maintenance costs of SPL products by using the concept Software as a Service. The SPL-SaaS approach was developed with the experiences of arvato services integrating the software product line concept since years. It shows up the advantageous and disadvantageous characteristics of components that play a role for the concept combination. To be able to identify adequate components, criteria for the identification of software components suitable for the approach are derived from these characteristics. Furthermore the requirements of the potential service users are examined and categorized concerning their effects on the system architecture. Special requirements of customers often lead to architectural constraints that are not compatible with the approach. If both, the criteria are met and the architectural constraints are compatible, the SPL-SaaS approach can be applied to a component. The whole approach is applied on an example of arvato services}
}

@inproceedings{Soltenborn2009b,
  author = {Gregor Engels AND Daniela Fisseler AND Christian Soltenborn},
  title = {Improving Reusability of Dynamic Meta Modeling Specifications with Rule Overriding},
  booktitle = {Proceedings of the 2009 IEEE Symposium on Visual Languages and Human-Centric Computing (VL/HCC 2009), Corvallis, Oregon (USA)},
  year = {2009},
  editor = {R. DeLine, M. Minas, M. Erwig},
  pages = {39--46},
  publisher = {IEEE Computer Society},
  address = {Piscataway, NJ (USA)},
  abstract = {Dynamic Meta Modeling (DMM) is a visual semantics specification technique targeted at languages equipped with a metamodel. In DMM, the metamodel of a language is mapped into a runtime metamodel able to express runtime states of instances of that language. In addition, graph transformation rules are defined which describe how these runtime states change in time. Given an instance of the runtime metamodel and a set of rules typed over that metamodel, a transition system can be computed which represents the semantics of the model instance under investigation.To be easily understandable by language engineers, DMM resembles a couple of well-known object-oriented concepts. Part of this is the fact that a DMM rule has many similarities to a method in an object-oriented language.In this paper, we enhance DMM such that DMM rules can "override" other DMM rules, similar to a method being overridden in a subclass. We argue that this does not only have positive impact on reusability of DMM specifications, but also improves the intuitive understandability of DMM rules.}
}

@inproceedings{EngSaSa09,
  author = {Frank Salger AND Stefan Sauer AND Gregor Engels},
  title = {Integrated Specification and Quality Assurance for Large Business Information Systems},
  booktitle = {Proceedings of the 2nd India Software Engineering Conference (ISEC'09)},
  year = {2009},
  pages = {129--130},
  publisher = {ACM Press},
  address = {New York, NY, USA}
}

@inproceedings{GerthModels09,
  author = {Christian Gerth AND Jochen K{\"u}ster AND Gregor Engels},
  title = {Language-Independent Change Management of Process Models},
  booktitle = {Proceedings of the ACM/IEEE 12th International Conference on Model Driven Engineering Languages and Systems (MODELS'09). Denver (CO, USA)},
  year = {2009},
  editor = {A. Sch{\"u}rr, B. Selic},
  pages = {152--166},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  abstract = {In model-driven development approaches, process models are used at different levels of abstraction and are described by different languages. Similar to other software artifacts, process models are developed in team environments and underlie constant change. This requires reusable techniques for the detection of changes between different process models and the computation of dependencies and conflicts between changes. In this paper, we propose a framework for the construction of process model change management solutions that provides generic techniques for the detection of differences and the computation of dependencies and conflicts between changes. The framework contains an abstract representation for process models that serves as a common denominator for different process models. In addition, we show how the framework is instantiated exemplarily for BPMN.}
}

@inproceedings{seaa09/mde,
  author = {Baris G{\"u}ldali AND Michael Mlynarski AND Andreas W{\"u}bbeke AND Gregor Engels},
  title = {Model-Based System Testing Using Visual Contracts},
  booktitle = {Proceedings of Euromicro SEAA Conference 2009, Special Session on “Model Driven Engineering”},
  year = {2009},
  pages = {121-124},
  publisher = {IEEE Computer Society},
  address = {Washington, DC, USA}
}

@inproceedings{gse+09,
  author = {Baris G{\"u}ldali AND Holger Funke AND Michael Jahnich AND Stefan Sauer AND Gregor Engels},
  title = {Semi-automated Test Planning for e-ID Systems by Using Requirements Clustering},
  booktitle = {24th IEEE/ACM International Conference on Automated SoftwareEngineering (ASE 2009), 16-20 November 2009, Auckland, New Zeland},
  year = {2009},
  pages = {29-39}
}

@inproceedings{EGPS09,
  author = {Gregor Engels AND Silke Geisen AND Stefan Sauer AND Olaf Port},
  title = {Sicherstellen der Betrachtung von nicht-funktionalen Anforderungen in SCRUM-Prozessen durch Etablierung von Feedback},
  booktitle = {Informatik 2009 - Im Focus das Leben},
  year = {2009},
  editor = {Stefan Fischer, Erik Maehle, R{\"u}diger Reischuk},
  pages = {458}
}

@inproceedings{Soltenborn2009a,
  author = {Christian Soltenborn AND Gregor Engels},
  title = {Towards Test-Driven Semantics Specification},
  booktitle = {Proceedings of the 12th International Conference on Model Driven Engineering Languages and Systems (MODELS 2009), Denver, Colorado (USA)},
  year = {2009},
  editor = {A. Sch{\"u}rr, B. Selic},
  pages = {378--392},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  abstract = {Behavioral models are getting more and more important within the software development cycle. To get the most use out of them, their behavior should be defined formally. As a result, many approaches exist which aim at specifying formal semantics for behavioral languages (e.g., Dynamic Meta Modeling (DMM), Semantic Anchoring). Most of these approaches give rise to a formal semantics which can e.g. be used to check the quality of a particular language instance, for instance using model checking techniques.However, if the semantics specification itself contains errors, it is more or less useless, since one cannot rely on the analysis results. Therefore, the language engineer must make sure that the semantics he develops is of the highest quality possible. To help the language engineer to achieve that goal, we propose a test-driven semantics specification process: the semantics of the language under consideration is first informally demonstrated using example models, which will then be used as test cases during the actual semantics specification process. In this paper, we present this approach using the already mentioned specification language DMM.}
}

@inproceedings{Engels08-1,
  author = {Gregor Engels AND Andreas Hess AND Bernhard Humm AND Oliver Juwig AND Marc Lohmann AND Jan-Peter Richter AND Markus Voß AND Johannes Willkomm},
  title = {A Method for Engineering a true Service-Oriented Architecture},
  booktitle = {Proceedings of the Tenth International Conference on Enterprise Information Systems (ICEIS 2008), Barcelona (Spain)},
  year = {2008},
  editor = {J. Cordeiro, J. Filipe},
  pages = {272--281},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  month = {June },
  note = {10th International Conference on Enterprise Information Systems (ICEIS 2008)}
}

@inproceedings{Kuester08,
  author = {Jochen K{\"u}ster AND Christian Gerth AND Alexander F{\"o}rster AND Gregor Engels},
  title = {A Tool for Process Merging in Business-Driven Development},
  booktitle = {Proceedings of the Forum at the CAiSE'08 Conference on Advanced Information Systems Engineering},
  year = {2008},
  editor = {Z. Bellahsène, R. Coletta, X. Franch, E. Hunt, C. Woo},
  pages = {89--92},
  publisher = {CEUR-WS.org},
  abstract = {Business-driven development favors the construction of process modelsat different abstraction levels and by different people. As a consequence, thereis a demand for consolidating different versions of process models by mergingthem. In this paper, we study a basic scenario, derive requirements and present aprototype for detecting and resolving changes between process models.}
}

@inproceedings{Engels08,
  author = {Gregor Engels AND Baris G{\"u}ldali AND Christian Soltenborn AND Heike Wehrheim},
  title = {Assuring Consistency of Business Process Models and Web Services using Visual Contracts},
  booktitle = {Proceedings of the 3rd International Symposium on Applications of Graph Transformation with Industrial Relevance (AGTIVE 2007), Kassel (Germany)},
  year = {2008},
  editor = {A. Sch{\"u}rr, M. Nagl, A. Z{\"u}ndorf},
  pages = {17--31},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  month = {October},
  abstract = {Business process models describe workflows by a set of actions together with their ordering. When implementing business processes within a service-oriented architecture, these actions are mapped to existing IT (web) services, which are then to be executed in the order specified by the business process. However, the execution of a web service can require certain preconditions to be fulfilled. These might not hold at the time of execution specified in the business process model: it can be inconsistent with the web service specification.In this paper we propose a technique for checking consistency of process models with web service specifications. To this end, both are equipped with a formal semantics (in terms of graph transformations). We show how to use an existing model checker for graph transformation systems to carry out the consistency check.}
}

@inproceedings{Comp08,
  author = {Frank Salger AND Marcel Bennicke AND Gregor Engels AND Claus Lewerentz},
  title = {Comprehensive Architecture Evaluation and Management in Large Software-Systems},
  booktitle = {Quality of Software Architectures. Models and Architectures},
  year = {2008},
  editor = {S. Becker, F. Plasil, R. Reussner},
  pages = {205--219},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  month = {October},
  abstract = {The architecture of a software system is both a success and a failure factor. Taking the wrong architectural decisions may break a project, since such errors are often systematic and affect cross-cutting aspects of the system to be built. Moreover, software projects get more and more challenging due to the rising complexity and dynamics of business processes, large team size and distributed development. As the software architecture is the common platform for many project activities, it constitutes a critical success factor. Thus, a comprehensive method for evaluating a software architecture and propagating important properties of it downstream to code is needed. At sd&m, we designed a comprehensive architecture evaluation and management framework in order to satisfy these needs. In this paper, we derive a list of requirements, such a framework should fulfill. We then present the components of our architecture evaluation method and demonstrate, how it fulfills these requirements.}
}

@inproceedings{DetKGFE08,
  author = {Jochen K{\"u}ster AND Christian Gerth AND Alexander F{\"o}rster AND Gregor Engels},
  title = {Detecting and Resolving Process Model Differences in the Absence of a Change Log},
  booktitle = {Proceedings of the 6th International Conference on Business Process Management (BPM'08)},
  year = {2008},
  editor = {M. Dumas, M. Reichert, M.-C. Shan},
  pages = {244--260},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  abstract = {Business-driven development favors the construction of process models at different abstraction levels and by different people. As a consequence, there is a demand for consolidating different versions of process models by detecting and resolving differences. Existing approaches rely on the existence of a change log which logs the changes when changing a process model. However, in several scenarios such a change log does not exist and differences must be identified by comparing process models before and after changes have been made. In this paper, we present our approach to detecting and resolving differences between process models, in the absence of a change log. It is based on computing differences and deriving change operations for resolving differences, thereby providing a foundation for variant and version management in these cases.}
}

@inproceedings{VE08-2,
  author = {Hendrik Voigt AND Gregor Engels},
  title = {Ein verfeinerter GQM-Ansatz zur Qualit{\"a}tsbewertung von Software-Modellen},
  booktitle = {Proceedings of Software-Qualit{\"a}tsmodellierung und -bewertung (SQMB '08), M{\"u}nchen, Germany},
  year = {2008},
  editor = {S. Wagner, M. Broy, F. Deissenboeck, J. M{\"u}nch, P. Liggesmeyer},
  pages = {39--46},
  publisher = {Technische Universit{\"a}t M{\"u}nchen},
  abstract = {Wir stellen einen Qualit{\"a}tsmanagementansatz zur Bewertung von Software-Modellen vor. Unser Ansatz basiert auf der Goal Question Metric (GQM). Wir verfeinern GQM und f{\"u}gen wichtige Konzepte und Aktivit{\"a}ten hinzu, um auf diese Weise die Besonderheiten bei der Qualit{\"a}tsbewertung von Software-Modellen ber{\"u}cksichtigen zu k{\"o}nnen. Dabei konzentrieren wir uns insbesondere auf den Kontext eines Software-Modells als entscheidenden Einflussfaktor f{\"u}r die Dokumentation von Informationsbed{\"u}rfnissen, Qualit{\"a}tsverst{\"a}ndnis, Messung und Analyse. Aktuell wird eine Werkzeugunterst{\"u}tzung f{\"u}r die Eclipse Plattform entwickelt, damit unser Qualit{\"a}tsmanagementansatz evaluiert und wirtschaftlich eingesetzt werden kann.}
}

@inproceedings{Engels08-2,
  author = {Gregor Engels AND Anneke Kleppe AND Arend Rensink AND Maria Semenyak AND Christian Soltenborn AND Heike Wehrheim},
  title = {From UML Activities to TAAL - Towards Behaviour-Preserving Model Transformations},
  booktitle = {Proceedings of the 4th European Conference on Model Driven Architecture - Foundations and Applications (ECMDA-FA 2008), Berlin (Germany)},
  year = {2008},
  editor = {I. Schieferdecker, A. Hartman},
  pages = {95--109},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  month = {July},
  abstract = {Model transformations support a model-driven design by providing an automatic translation of abstract models into more concrete ones, and eventually program code. Crucial to a successful application of model transformations is their correctness, in the sense that the meaning (semantics) of the models is preserved. This is especially important if the models not only describe the structure but also the intended behaviour of the systems. Reasoning about and showing correctness is, however, often impossible as the source and target models typically lack a precise definition of their semantics.In this paper, we take a first step towards provably correct behavioural model transformations. In particular, we develop transformations from UML Activities (which are visual models) to programs in TAAL, which is a textual Java-like programming language. Both languages come equipped with formal behavioural semantics, which, moreover, have the same semantic domain. This sets the stage for showing correctness, which in this case comes down to showing that the behaviour of every (well-formed) UML Activity coincides with that of the corresponding TAAL program, in a well-defined sense.}
}

@inproceedings{VE08-1,
  author = {Hendrik Voigt AND Gregor Engels},
  title = {Kontextsensitive Qualit{\"a}tsplanung f{\"u}r Software-Modelle},
  booktitle = {Proceedings of Modellierung (2008), Berlin (Germany)},
  year = {2008},
  editor = {T. K{\"u}hne, W. Reisig, F. Steimann},
  pages = {165--180},
  publisher = {GI},
  month = {March},
  abstract = {Der Goal Question Metric (GQM) Ansatz stellt eine allgemeine Qualit{\"a}tsmanagementstrategie dar und ber{\"u}cksichtigt infolgedessen nicht die Besonderheiten von Software-Modellen. Wir haben eine kontextsensitive Qualit{\"a}tsplanung f{\"u}r Software- Modelle entwickelt, die den GQM-Ansatz auf die Qualit{\"a}tsplanung von Software- Modellen zuschneidet und um Konzepte und Aktivit{\"a}ten erweitert. Dabei konzentrieren wir uns auf den Kontext eines Software-Modells als entscheidenden Einflussfaktor f{\"u}r die Dokumentation von Informationsbed{\"u}rfnissen, Qualit{\"a}tsverst{\"a}ndnis und Messung. Unser Ansatz zur Qualit{\"a}tsplanung besteht aus einem Metamodell zur Formulierung relevanter Inhalte und einem Prozess, der als Leitfaden bei der Planung dient.}
}

@inproceedings{VGE08,
  author = {Hendrik Voigt AND Baris G{\"u}ldali AND Gregor Engels},
  title = {Quality Plans for Measuring the Testability of Models},
  booktitle = {Proceedings of the 11th International Conference on Quality Engineering in Software Technology (CONQUEST 2008), Potsdam (Germany)},
  year = {2008},
  editor = {I. Schieferdecker, S. Goericke},
  pages = {353--370},
  publisher = {dpunkt.verlag},
  abstract = {For models used in model-based testing, the evaluation of their testability is an important issue. Existing approaches lack some relevant aspects for a systematic and comprehensive evaluation. Either they do (1) not consider the context of software models, (2) not offer a systematic process for selecting and developing right measurements, (3) not define a consistent and common quality understanding, or (4) not distinct between objective and subjective measurements.We present a novel quality management approach for the evaluation of software models in general that considers all these aspects in an integrated way. Our approach is based on a combination of the Goal Question Metric (GQM) and quality models. We demonstrate our approach by systematically developing a short quality plan for measuring the testability of software models.}
}

@inproceedings{DBLP:conf/se/EngelsV08,
  author = {Gregor Engels AND Markus Voß},
  title = {Quasar Enterprise - Anwendungslandschaften serviceorientiert gestalten},
  booktitle = {Software Engineering 2008. Fachtagung des GI-Fachbereichs Softwaretechnik},
  year = {2008},
  editor = {K. Herrmann, B. Bruegge},
  pages = {24--27},
  publisher = {GI},
  month = {February }
}

@inproceedings{Frohnhoff08,
  author = {Stephan Frohnhoff AND Gregor Engels},
  title = {Revised Use Case Point Method - Effort Estimation in Development Projects for Business Applications},
  booktitle = {Setting Quality Standards, Proceedings of the 11th International Conference on Quality Engineering in Software Technology (CONQUEST 2008), Potsdam (Germany)},
  year = {2008},
  editor = {I. Schieferdecker, S. Goericke},
  pages = {15--32},
  publisher = {dpunkt Verlag},
  abstract = {Rapid and precise effort estimation of software development projects is crucial in ITindustry. In a case study, the Use Case Point (UCP) method was applied to 15 commercialsoftware development projects. The estimated efforts were compared with the incurredproject efforts. We measured a standard deviation of 42 %. This is not acceptablefor industrial usage. Therefore, we propose appropriate improvements of the UseCase Point method leading to significantly higher estimation accuracy with only 20 %standard deviation. The contribution of this paper is a detailed description of the improvedUse Case Point method.}
}

@inproceedings{AssEDOC08,
  author = {Martin Assmann AND Gregor Engels},
  title = {Service-Oriented Enterprise Architectures: Evolution of Concepts and Methods},
  booktitle = {Proc. of the 12th IEEE International Enterprise Distributed Object Computing Conference 2008 (EDOC 08), Munich (Germany)},
  year = {2008},
  pages = {xxxiv--xliii},
  publisher = {IEEE Computer Society},
  address = {Washington, DC, USA},
  month = {September},
  abstract = {This paper depicts the evolution of enterprise architectures to their today often used service-oriented form and presents a state-of-the-art development process for this kind of architecture. The development process covers both the development of business architecture as well as the appropriate software architecture. While showing up a possible form of further evolution of enterprise architectures, we identify the major challenges for future development methods of enterprise architectures.}
}

@inproceedings{AssmannEcsa08,
  author = {Martin Assmann AND Gregor Engels},
  title = {Transition to Service-Oriented Enterprise Architecture},
  booktitle = {Proceedings of the Second European Conference on Software Architecture (ECSA 2008), Paphos (Cyprus)},
  year = {2008},
  editor = {R. Morrison, D. Balasubramaniam, K. E. Falkner},
  pages = {346--349},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  month = {September},
  abstract = {Enterprise Architecture (EA) has undergone many changes since the IT has found its way into enterprises. At the moment the Service-Oriented Architecture (SOA) is being hyped but has also gained some importance. Implementing SOA can have many implications for an enterprise, depending on how visionary the implemented architecture is. This paper provides the description of an enterprise architecture that is fully-fledged concerning service-orientation and points out the architectural challenges that have to be mastered with future research results.}
}

@inproceedings{Schattkowsky2007a,
  author = {Tim Schattkowsky AND Gregor Engels AND Alexander F{\"o}rster},
  title = {A Model-Based Approach for Platform-Independent Binary Components with Precise Timing and Fine-Grained Concurrency},
  booktitle = {Proceedings of the 40th Annual Hawaii International Conference on System Sciences (HICSS 2007)},
  year = {2007},
  pages = {286ff.},
  publisher = {IEEE Computer Society},
  address = {Washington, DC, USA},
  abstract = {Fine grained concurrency and accurate timing can be essential for embedded hardware and software systems. These requirements should be reflected in the specification and must be consistently enforced by the actual implementation. Automated synthesis of the implementation from such specifications appears to be a straightforward way to ensure this consistency. However, especially for software systems this is quite difficult, since software lacks the inherent timing and concurrency of a hardware system. Still, the same timing and concurrency requirements have to be fulfilled. Thus, we introduce a UML-based design approach that supports the synthesis of embedded hardware or software systems from essentially the same abstract specification. Our approach provides explicit support for specifying fine grained concurrency and microsecond accurate timing. In our approach, these properties must be ensured by the automatically derived implementation. Since this is especially hard to achieve for software systems, this paper focuses on execution on software platforms. For this, we introduce our UML Virtual Machine (UVM). It enables the direct execution of binary encoded system specifications and enforces the desired timing and concurrency. As a result, our approach enables the creation of binary encoded portable concurrent time-accurate software components.}
}

@inproceedings{Engels2007a,
  author = {Gregor Engels AND Christian Soltenborn AND Heike Wehrheim},
  title = {Analysis of UML Activities Using Dynamic Meta Modeling},
  booktitle = {Proceedings of the conference on Formal Methods for Open Object-based Distributed Systems (FMOODS 2006), Oslo (Norway)},
  year = {2007},
  editor = {M. M. Bosangue, E. Broch Johnsen},
  pages = {76--90},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  month = {June},
  abstract = {Dynamic Meta Modeling (DMM) is a universal approach to defining semantics for languages syntactically grounded on meta models. DMM has been designed with the aim of getting highly understandable yet precise semantic models which in particular allow for a formal analysis. In this paper, we exemplify this by showing how DMM can be used to give a semantics to and define an associated analysis technique for UML Activities.}
}

@inproceedings{Soltenborn2006,
  author = {Christian Soltenborn AND Gregor Engels},
  title = {Analysis of UML Activities with Dynamic Meta Modeling Techniques},
  booktitle = {Symposium "A Formal Semantics for UML" (satellite event of the MoDELS conference 2006), Genova (Italy)},
  year = {2007},
  editor = {T. K{\"u}hne},
  pages = {329--330},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  abstract = {Based on a semantics of UML Activities specified with the Dynamic Meta Modeling approach, we analyze the dynamic semantics of Activities at modeling time.}
}

@inproceedings{Sauer2007,
  author = {Stefan Sauer AND Gregor Engels},
  title = {Easy Model-Driven Development of Multimedia User Interfaces with GuiBuilder},
  booktitle = {Proceeding of the 4th International Conference on Universal Access in Human-Computer Interaction (UAHCI, as Part of HCI International, 2007), Beijing (China)},
  year = {2007},
  editor = {C. Stephanidis},
  pages = {537--546},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  note = {Journal:Universal Access in HCI, Part IBook:HCI (5)},
  abstract = {GUI builder tools are widely used in practice to develop the user interface of software systems. Typically they are visual programming tools that support direct-manipulative assembling of the user interface components. We have developed the tool GuiBuilder which follows a model-driven approach to the development of graphical (multimedia) user interfaces. This allows a meta-design approach where user interface developers as well as prospective users of the system are supported in modelling the desired functionality of the GUI on a high level of abstraction that is easy to understand for all involved stakeholders. The model consists of compositional presentation diagrams to model the structure of the user interface and hierarchical statechart diagrams to model its behaviour. GuiBuilder then supports the transformation of the model to Java, i.e., the generation of a working user interface and the simulation of the modelled behaviour. Interactive sessions with the user interface can be recorded and replayed.}
}

@inproceedings{Hess2007,
  author = {Andreas Hess AND Bernhard Humm AND Markus Voß AND Gregor Engels},
  title = {Structuring Software Cities - A Multidimensional Approach},
  booktitle = {Proceedings of the 11th IEEE International Enterprise Distributed Object Computing Conference (EDOC 2007)},
  year = {2007},
  pages = {122--129},
  publisher = {IEEE Computer Society},
  address = {Washington, DC, USA},
  abstract = {Software cities alias application landscapes of large enterprises comprise tens or even hundreds of IT applications. Structuring software cities into domains is an important task of enterprise architects. The quality of the resulting domain model is crucial for the success of enterprise architecture management and an important tool for the governance of the development of an enterprise's application landscape. This paper presents a novel method for constructing domain models based on business services, business objects, and business dimensions. The method has been validated in numerous industrial projects. }
}

@inproceedings{Forster2007,
  author = {Alexander F{\"o}rster AND Gregor Engels AND Tim Schattkowsky AND Ragnhild Van Der Straeten},
  title = {Verification of Business Process Quality Constraints Based on Visual Process Patterns},
  booktitle = {Proceedings of the First Joint IEEE/IFIP Symposium on Theoretical Aspects of Software Engineering (TASE 2007), Shanghai (China)},
  year = {2007},
  pages = {197--208},
  publisher = {IEEE Computer Society},
  address = {Washington, DC, USA},
  abstract = {Business processes usually have to consider certain constraints like domain specific and quality requirements. The automated formal verification of these constraints is desirable, but requires the user to provide an unambiguous formal specification. In particular since the notations for business process modeling are usually visual flow-oriented languages, the notational gap to the languages usually employed for the formal specification of constraints, e.g., temporal logic, is significant and hard to bridge. Thus, our approach relies on UML Activities as a single language for the specification of both business processes and the corresponding constraints. For the expression of such constraints, we have provided a process pattern definition language based on specialized Activities. In this paper, we describe how model checking can be employed for formal verification of business processes against such patterns. For this, we present an automated transformation of the business process and the corresponding patterns into a transition system and temporal logic, respectively.}
}

@inproceedings{FoersterVLHCC06,
  author = {Alexander F{\"o}rster AND Tim Schattkowsky AND Gregor Engels AND Ragnhild Van Der Straeten},
  title = {A Pattern-driven Development Process for Quality Standard-conforming Business Process Models},
  booktitle = {IEEE Symposium on Visual Languages and Human-Centric Computing (VL/HCC 2006), Brighton (UK)},
  year = {2006},
  pages = {135--142},
  publisher = {IEEE Computer Society},
  address = {Washington, DC, USA}
}

@inproceedings{Engels2006d,
  author = {Gregor Engels AND Baris G{\"u}ldali AND Oliver Juwig AND Marc Lohmann AND Jan-Peter Richter},
  title = {Industrielle Fallstudie: Einsatz visueller Kontrakte in serviceorientierten Architekturen},
  booktitle = {Proceedings of the conference on Software Enginneering, Fachtagung des GI Fachbereichs Softwaretechnik (SE 2006), Leipzig (Germany)},
  year = {2006},
  editor = {B. Biel, M. Book, V. Gruhn},
  pages = {111--122},
  publisher = {K{\"o}llen Druck + Verlag GmbH},
  address = {Bonn},
  month = {March},
  note = {Software Enginneering 2006, Fachtagung des GI Fachbereichs Softwaretechnik},
  abstract = {Serviceorientierte Architekturen (SOA) erlauben eine schnelle und kosteneffiziente Bereitstellung unterschiedlicher Funktionalit{\"a}ten zur Unterst{\"u}tzung der Gesch{\"a}ftsprozesse eines Unternehmens. Dazu werden fachliche Funktionalit{\"a}ten in Form von Enterprise Services zur Verf{\"u}gung gestellt. Die hohe Zahl von Enterprise Services erfordert eine geeignete semantische Beschreibung zu deren effizienten Verwaltung. Zur semantischen Beschreibung von Enterprise Services sowie zur Formulierung von Suchanfragen ist an der Universit{\"a}t Paderborn die Methode der visuellen Kontrakte entwickelt worden. Das Papier stellt die Ergebnisse der ersten Phase einer umfangreichen industriellen Fallstudie zur Evaluation der praktischen Anwendbarkeit visueller Kontrakte im Kontext einer SOA vor.}
}

@inproceedings{Engels2006f,
  author = {Gregor Engels AND Marc Lohmann AND Stefan Sauer AND Reiko Heckel},
  title = {Model-Driven Monitoring: An Application of Graph Transformation for Design by Contract},
  booktitle = {Proceedings of the 3rd International Conference on Graph Transformation (ICGT 2006), Natal (Brazil)},
  year = {2006},
  editor = {A. Corradini, H. Ehrig, U. Montanari, L. Ribeiro, G. Rozenberg},
  pages = {336--350},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  abstract = {The model-driven development (MDD) approach for constructing software systems advocates a stepwise refinement and transformation process starting from high-level models to concrete program code. In contrast to numerous research efforts that try to generate executable function code from models, we propose a novel approach termed model-driven monitoring. Here, models are used to specify minimal requirements and are transformed into assertions on the code level for monitoring hand-coded programs during execution.We show how well-understood results from the graph transformation community can be deployed to support this model-driven monitoring approach. In particular, models in the form of visual contracts are defined by graph transitions with loose semantics, while the automatic transformation from models to JML assertions on the code level is defined by strict graph transformation rules. Both aspects are supported and realized by a dedicated Eclipse plug-in.}
}

@inproceedings{Lohmann2006a,
  author = {Marc Lohmann AND Gregor Engels AND Stefan Sauer},
  title = {Model-driven Monitoring: Generating Assertions from Visual Contracts},
  booktitle = {Proceedings of the 21st IEEE International Conference on Automated Software Engineering (ASE 06), Tokyo (Japan)},
  year = {2006},
  pages = {355--356},
  publisher = {IEEE Computer Society},
  address = {Los Alamitos, CA, USA},
  abstract = {The Visual Contract Workbench is a tool that supports model-driven development of software systems by lifting the Design by Contract idea, which is usually used at the code level, to the model level. It uses visual contracts for graphically specifying the pre- and post-conditions of an operation. Java classes with JML (Java Modeling Language) assertions are generated from visual contracts to facilitate automatic monitoring of the correctness of the programmer's implementation.}
}

@inproceedings{Engels2006e,
  author = {Gregor Engels AND Jan Hendrik Hausmann AND Marc Lohmann AND Stefan Sauer},
  title = {Teaching UML Is Teaching Software Engineering Is Teaching Abstraction},
  booktitle = {Proceedings of the Satellite Events at the MoDELS 2005 Conference, Montego Bay (Jamaica)},
  year = {2006},
  editor = {J.-M. Bruel},
  pages = {306--319},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  month = {October},
  note = {Proceedings of the workshopt on Satellite Events at the MoDELS 2005 Conference (MoDELS 2005 International Workshops OCLWS, MoDeVA, MARTES, AOM, MTiP, WiSME, MODAUI, NfC, MDD, WUsCAM, Montego Bay, Jamaica)},
  abstract = {As the Unified Modeling Language (UML) has by now seen widespread and successful use in the software industry and academia alike, it has also found its way into many computer science curricula. An outstanding advantage of teaching UML is that it enables an illustration of many crucial concepts of software engineering, far beyond its concrete notation. Most important among these concepts is that of abstraction. We present a course design which demonstrates the use of UML as a vehicle for teaching such core concepts of software engineering. Multimedia elements and tools help to efficiently convey the courses message to the students.}
}

@inproceedings{Schattkowsky2006c,
  author = {Tim Schattkowsky AND Jan Hendrik Hausmann AND Gregor Engels},
  title = {Using UML Activities for System-on-Chip Design and Synthesis},
  booktitle = {Proceedings of the International Conference on Model Driven Engineering Languages and Systems (MoDELS 2006), Genova (Italy)},
  year = {2006},
  editor = {O. Nierstrasz, J. Whittle, D. Harel, G. Reggio},
  pages = {737--752},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  abstract = {The continuous advances in manufacturing Integrated Circuits (ICs) enable complete systems on a single chip. However, the design effort for such System-on-Chip (SoC) solutions is significant. The productivity of the design teams currently lags behind the advances in manufacturing and this design productivity gap is still widening. One important reason is the lack of abstraction in traditional Hardware Description Languages (HDLs) like VHDL. The UML provides more abstract concepts for modeling behavior that can also be employed for hardware design. In particular, the new UML Activity semantics fit nicely with the inherent data flow in hardware systems. Therefore, we introduce a UML-based design approach for complete SoC specification. Our approach enables generation of complete synthesizable HDL code. The equivalent hardware can be automatically generated using the existing tools chains. As an example, we outline Handel-C code generation for an MP3 decoder design.}
}

@inproceedings{Foerster2005,
  author = {Alexander F{\"o}rster AND Gregor Engels AND Tim Schattkowsky},
  title = {Activity Diagram Patterns for Modeling Quality Constraints in Business Processes},
  booktitle = {Proceedings of the 8th International Conference on Model Driven Engineering Languages and Systems (MoDELS 2005), Montego Bay (Jamaica)},
  year = {2005},
  editor = {L. C. Briand, C. Williams},
  pages = {2--16},
  publisher = {Springer},
  address = {Berlin/Heidelberg}
}

@inproceedings{Guo2005,
  author = {Ping Guo AND Gregor Engels AND Reiko Heckel},
  title = {Architectural Style - Based Modeling and Simulation of Complex Software Systems},
  booktitle = {Proceedings of the 12th Asia-Pacific Software Engineering Conference (APSEC 2005), Taipei (Taiwan)},
  year = {2005},
  pages = {367--374},
  publisher = {IEEE Computer Society},
  address = {Washington, DC, USA},
  month = {December},
  abstract = {The design and development of complex software systems is a difficult task, and it is not easy to ensure the quality of a developed software. The paper presents an architectural style-based approach to specifying and analyzing complex software systems. The approach is developed based on UML-like meta models and graph transformation techniques to support sound methodological principals, formal analysis and refinement. The approach is illustrated through the specification and simulation of architectural styles of mobile computing middleware, where three abstract levels of architectural styles are defined in order to decrease the complexity brought by mobility.}
}

@inproceedings{Engels2005d,
  author = {Gregor Engels AND Martin Erwig},
  title = {ClassSheets: automatic generation of spreadsheet applications from object-oriented specifications},
  booktitle = {Proceedings of the 20th IEEE/ACM International Conference on Automated Software Engineering (ASE 2005), Long Beach, CA (USA)},
  year = {2005},
  pages = {124--133},
  publisher = {ACM Press},
  address = {New York, NY, USA},
  month = {November},
  abstract = {Spreadsheets are widely used in all kinds of business applications.Numerous studies have shown that they contain manyerrors that sometimes have dramatic impacts. One reasonfor this situation is the low-level, cell-oriented developmentprocess of spreadsheets.We improve this process by introducing and formalizinga higher-level object-oriented model termed ClassSheet.While still following the tabular look-and-feel of spreadsheets,ClassSheets allow the developer to express explicitlybusiness object structures within a spreadsheet, whichis achieved by integrating concepts from the UML (UnifiedModeling Language). A stepwise automatic transformationprocess generates a spreadsheet application that is consistentwith the ClassSheet model. Thus, by deploying theformal underpinning of ClassSheets, a large variety of errorscan be prevented that occur in many existing spreadsheetapplications today.The presented ClassSheet approach links spreadsheet applicationsto the object-oriented modeling world and advocatesan automatic model-driven development process forspreadsheet applications of high quality.}
}

@inproceedings{Lohmann2005,
  author = {Marc Lohmann AND Stefan Sauer AND Gregor Engels},
  title = {Executable Visual Contracts},
  booktitle = {Proceedings of the IEEE Symposium on Visual Languages and Human-Centric Computing (VL/HCC 2005)},
  year = {2005},
  editor = {M. Erwig, A. Sch{\"u}rr},
  pages = {63--70},
  publisher = {IEEE Computer Society},
  address = {Washington, DC, USA},
  abstract = {Design by Contract (DbC) is widely acknowledged to be a powerful technique for creating reliable software. DbC allows developers to specify the behavior of an operation precisely by pre- and post-conditions. Existing DbC approaches predominantly use textual representations of contracts to annotate the actual program code with assertions. In the Unified Modeling Language (UML), the textual Object Constraint Languages (OCL) supports the specification of pre- arid post-conditions by constraining the model elements that occur in UML diagrams. However; textual specifications in OCL can become complex and cumbersome, especially for software developers who are typically not used to OCL. In this paper, we propose to specify the pre- and post-conditions of an operation visually by a pair of UML object diagrams (visual Contract). We define a mapping of visual contracts into Java classes that are annotated with behavioral interface specifications in the Java Modeling Language (JML). The mapping supports testing the correctness of the implementation against the specification using JML tools, which include a runtime assertion checker. Thus we make the visual contracts executable.}
}

@inproceedings{Engels06,
  author = {Gregor Engels AND Jan Hendrik Hausmann AND Marc Lohmann AND Stefan Sauer},
  title = {Teaching UML is Teaching Software Engineering is Teaching Abstraction},
  booktitle = {Proceedings of the Educators' Symposium of the MoDELS/UML 2005, Montego Bay (Jamaica)},
  year = {2005},
  editor = {H. Giese, P. Roques},
  pages = {306--319},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  month = {October},
  abstract = {As the Unified Modeling Language (UML) has by now seen widespread and successful use in the software industry and academia alike, it has also found its way into many computer science curricula. An outstanding advantage of teaching UML is that it enables an illustration of many crucial concepts of software engineering, far beyond its concrete notation. Most important among these concepts is that of abstraction. We present a course design which demonstrates the use of UML as a vehicle for teaching such core concepts of software engineering. Multimedia elements and tools help to efficiently convey the course’s message to the students. }
}

@inproceedings{Engels04,
  author = {Gregor Engels AND Stefan Sauer},
  title = {Guest Editors' Introduction},
  booktitle = {International Journal of Software Engineering and Knowledge Engineering (IJSEKE)},
  year = {2004},
  editor = {G. Engels, S. Sauer},
  pages = {543--544},
  publisher = {World Scientific Publishing},
  month = {December}
}

@inproceedings{Kuster2003,
  author = {Jochen K{\"u}ster AND Gregor Engels},
  title = {Consistency Management within Model-Based Object-Oriented Development of Components},
  booktitle = {Proceedings of the conference on Formal Methods for Components and Objects (FMCO 2003), Leiden (Netherlands)},
  year = {2003},
  editor = {F. S. de Boer and M. M. Bonsangue and S. Graf and W. P. de Roever},
  pages = {157-176},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  month = {October},
  abstract = {The Unified Modeling Language (UML) favors the construction of models composed of several submodels, modeling the system components under development at different levels of abstraction and from different viewpoints. Currently, consistency of object-oriented models expressed in the UML is not defined in the UML language specification. This allows the construction of inconsistent UML models. Defining consistency of UML models is complicated by the fact that UML models are applied differently, depending on the application domain and development process. As a consequence, a form of consistency management is required that allows the software engineer to define, establish and manage consistency, tailored specifically to the development context. In recent years, we have developed a general methodology and tool support to overcome this problem. The methodology is based on a thorough study of the notion of consistency and has led to a generic definition of the notion of consistency. Our methodology itself aims at a step-wise systematic construction of a consistency management process, by providing a number of activities to be performed by the software engineer. It is complemented by a tool called Consistency Workbench which supports the software engineer in performing the methodology. In this paper, we provide an overview and summary of our approach.}
}

@inproceedings{KusterHE03,
  author = {Jochen K{\"u}ster AND Reiko Heckel AND Gregor Engels},
  title = {Defining and Validating Transformations of UML Models},
  booktitle = {Proceedings of the conference on Human Centric Computing Languages and Environments (HCC 2003), Auckland (New Zealand)},
  year = {2003},
  pages = {145--152},
  publisher = {IEEE Computer Society},
  address = {Washington, DC, USA},
  abstract = {With the success of the UML, the ability of transforming models into programs or formal specifications becomes a key to automated code generation or verification in the software development process. In this paper, we describe a concept for specifying model transformations by means of graph transformation rules on the UML meta model. In order to validate the termination and uniqueness of such transformations, we derive a number of sufficient criteria from basic results of the theory of graph transformation. This ensures that the rules can be executed automatically while, at the same time, providing a high-level visual model of the transformation.}
}

@inproceedings{Engels2003d,
  author = {Gregor Engels AND Stefan Sauer AND Bettina Neu},
  title = {Integrating software engineering and user-centred design for multimedia software developments},
  booktitle = {Proceedings of the conference on Human-Centric Computing Languages and Environments (HCC 2003), Auckland (New Zealand)},
  year = {2003},
  pages = {254--256},
  publisher = {IEEE Computer Society},
  address = {Washington, DC, USA},
  month = {October },
  abstract = {The object-oriented modeling of interactive multimedia applications in the OMMMA approach is designed to enable multimedia software developers to create comprehensive analysis and design models of multimedia software. For development of highly usable multimedia applications, this approach must be embedded in a more holistic development process that takes a user-oriented perspective on multimedia software development. In this paper, we elaborate on the differences between usercentred design activities and object-oriented software design activities and outline their integration in a comprehensive development process.}
}

@inproceedings{Engels2003c,
  author = {Gregor Engels AND Jochen K{\"u}ster AND Reiko Heckel AND Marc Lohmann},
  title = {Model Based Verification and Validation of Properties},
  booktitle = {Proceedings of the conference on Uniform Approaches to Graphical Process Specification Techniques (UNIGRA 2003, Satellite Event of the ETAPS 2003), Warsaw (Poland)},
  year = {2003},
  editor = {R. Bardohl, H. Ehrig},
  pages = {1--18},
  publisher = {Elsevier Science},
  month = {June},
  abstract = {One of the key issues in software development, like in all engineering problems, is to ensure that the product delivered meets its specification. Verification and validation are well-established techniques for ensuring the quality of a product within the overall software development lifecycle. With models being expressed in the Unified Modeling Language, the application of verification and validation is complicated. Firstly, concerning verification, a UML model is typically not the input language of a verification tool. Secondly, with regards to validation, a UML model is also not directly executable. In this paper, we show how verification and validation can be achieved for UML models. Within our approach, graph transformation techniques are applied for automated translation of UML models into a language understood by a verification tool or directly into an implementation. By the use of such semantic-preserving transformations, both verification and validation can be lifted up to the model level, allowing for a seamless integration of verification and validation into a UML-based development process.}
}

@inproceedings{Alfert2003,
  author = {Klaus Alfert AND Ernst-Erich Doberkat AND Gregor Engels AND Marc Lohmann AND Johannes Magenheim AND Andy Sch{\"u}rr},
  title = {MuSofT: Multimedia in der Softwaretechnik},
  booktitle = {Proceedings of the conference on Software Engineering im Unterricht der Hochschulen (SEUH 2003), Berlin (Germany)},
  year = {2003},
  editor = {J. Siedersleben, D. Weber-Wulff},
  pages = {70--80},
  publisher = {dpunkt Verlag},
  address = {Heidelberg},
  month = {February},
  note = {SEUH 8 - Software Engineering im Unterricht der Hochschulen, Berlin 2003},
  abstract = {Im BMBF-Verbundprojekt MuSofT werden multimediale Lehrmaterialien f{\"u}r die Lehre der Softwaretechnik entwickelt. In diesem Papier stellen wir die Bem{\"u}hungen innerhalb von MuSofT vor, eine qualitativ hochwertige und nachhaltige Entwicklung von Lernobjekten zu realisieren. Wir legen den Fo-kus dabei auf die didaktischen Grundannahmen, die inhaltliche und stilisti-sche Abstimmung zwischen den Materialien sowie die gleichf{\"o}rmige Be-schreibung der Materialien durch Metadaten, die eine effektive Recherche des Materials innerhalb des MuSofT-Portals erm{\"o}glichen.}
}

@inproceedings{Engels03,
  author = {Gregor Engels AND Klaus Alfert AND Ernst-Erich Doberkat},
  title = {MuSofT: Multimedia in der SoftwareTechnik},
  booktitle = {Proceeding of the 1. e-Learning Fachtagung Informatik (DeLFI 2003), Garching bei M{\"u}nchen (Germany)},
  year = {2003},
  editor = {A. Bode, J. Desel, S. Ratmayer, M. Wessner},
  pages = {115-119},
  publisher = {Gesellschaft f{\"u}r Informatik},
  month = {September }
}

@inproceedings{Engels2003b,
  author = {Gregor Engels AND Reiko Heckel AND Jochen K{\"u}ster},
  title = {The Consistency Workbench: A Tool for Consistency Management in UML-based Development},
  booktitle = {Proceedings of the 6th International Conference on The Unified Modeling Language: Modeling Languages and Applications (UML 2003), San Francisco, CA (USA)},
  year = {2003},
  editor = {P. Stevens, J. Whittle, G. Booch},
  pages = {356--359},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  abstract = {With the Unified Modeling Language becoming applied indiverse contexts, the ability of defining and checking customized consistencyconditions is gaining increasing importance. In this paper, weintroduce the Consistency Workbench for defining and establishing consistencyin a UML-based development process.}
}

@inproceedings{Engels02a,
  author = {Gregor Engels AND Reiko Heckel AND Jochen K{\"u}ster AND Luuk Groenewegen},
  title = {Consistency-Preserving Model Evolution through Transformations},
  booktitle = {Proceedings of the 5th International Conference on The Unified Modeling Language (UML 2002), Dresden (Germany)},
  year = {2002},
  editor = {J.-M. Jézéquel, H. Hussmann, S. Cook},
  pages = {212--226},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  month = {Oktober}
}

@inproceedings{Engels2002e,
  author = {Gregor Engels AND Jochen K{\"u}ster AND Luuk Groenewegen},
  title = {Consistent Interaction Of Software Components},
  booktitle = {Proceedings of the conference on Integrated Design and Process Technology (IDPT 2002), Pasadena, CA (USA)},
  year = {2002},
  pages = {2--22},
  publisher = {IOS Press},
  month = {June },
  abstract = {Constructing complex software systems by integrating different software components is a promising and challenging approach. With the functionality of software components given by models it is possible to ensure consistency of such models before implementation in order to successfully build the system. Models consisting of different submodels, the absence of an overall formal semantics and the numerous possibilities of employing models requires the development of techniques ensuring the consistency. In this paper, we discuss the issue of consistency of models made up of different submodels proposing a concept for the management of consistency. Consistency management relies on a consistency concept and a process for ensuring consistency of models. We introduce a consistency concept for software components modeled in the Unified Modeling Language (UML) and devise suitable consistency checks. On this basis, we propose a process how to locate and resolve inconsistencies, thus ensuring the consistency of models and by that the consistency of component-based systems derived from those models.}
}

@inproceedings{Depke2002,
  author = {Ralph Depke AND Gregor Engels AND Matthew Langham AND Bj{\"o}rn L{\"u}tkemeier AND Sebastian Th{\"o}ne},
  title = {Process-Oriented, Consistent Integration of Software Components},
  booktitle = {Proceedings of the conference on Prolonging Software Life: Development and Redevelopment (COMPSAC 2002), Oxford (England)},
  year = {2002},
  pages = {13--18},
  publisher = {IEEE Computer Society},
  address = {Washington, DC, USA},
  month = {August},
  note = {COMPSAC '02: Proceedings of the 26th International Computer Software and Applications Conference on Prolonging Software Life: Development and Redevelopment},
  abstract = {The integration of software components becomes a more and more important issue in software engineering. Process-oriented approaches should provide automated information processes. Therefore, the software components have to be integrated in a consistent way, i.e., their export interfaces have to be respected by the importing components. Furthermore, the type system of component interfaces has to support a tunable degree of freedom. This allows the insertion of components with interfaces of restricted but sufficient degree of compatibility. In this paper, we develop a concept for consistent and flexible integration of components. We present a process modeling language that combines UML and XML in order to support consistent, flexible, and executable processes. Finally, we provide a formalization of the proposed component type system.}
}

@inproceedings{Engels2002f,
  author = {Gregor Engels AND Jan Hendrik Hausmann AND Reiko Heckel AND Stefan Sauer},
  title = {Testing the Consistency of Dynamic UML Diagrams},
  booktitle = {Proceedings of the Sixth International Conference on Integrated Design and Process Technology (IDPT 2002), Pasadena, CA (USA)},
  year = {2002},
  month = {June},
  note = {Pasadena, CA, USA}
}

@inproceedings{EngelsKGH2001b,
  author = {Gregor Engels AND Jochen K{\"u}ster AND Luuk Groenewegen AND Reiko Heckel},
  title = {A methodology for specifying and analyzing consistency of object-oriented behavioral models},
  booktitle = {Proceedings of the 8th European Software Engineering Conference (ESEC 2001) and 9th ACM SIGSOFT Symposium on the Foundations of Software Engineering (FSE-9), Vienna (Austria)},
  year = {2001},
  editor = {V. Gruhn},
  pages = {186--195},
  publisher = {ACM Press},
  address = {New York, NY, USA},
  month = {September },
  abstract = {Object-oriented modeling favors the modeling of object behavior from different viewpoints and the successive refinement of behavioral models in the development process. This gives rise to consistency problems of behavioral models. The absence of a formal semantics for UML models and the numerous possibilities of employing behavioral models within the development process lead to the rise of a number of different consistency notions. In this paper, w e discuss the issue of consistency of behavioral models in the UML and present a general methodology how consistency problems can be dealt with. According to the methodology, those aspects of the models relevant to the consistency are mapped to a semantic domain in which precise consistency tests can be formulated. The choice of the semantic domain and the definition of consistency conditions can be used to construct different consistency notions. We show the applicability of our methodology by giving an example of a concrete consistency problem of concurrent object-oriented models.}
}

@inproceedings{HE01,
  author = {Reiko Heckel AND Gregor Engels},
  title = {Graph Transformation as a Meta Language for Dynamic Modeling and Model Evolution},
  booktitle = {Proceeding of International Special Session on Formal Foundations of Software Evolution (FFSE 2001, co-located with the Conference on Software Maintenance and Reengineering), Lisbon (Portugal)},
  year = {2001},
  editor = {T. Mens, M. Wermelinger},
  pages = {42-47},
  publisher = {Universidade Nova de Lisboa},
  address = {Lisbon}
}

@inproceedings{Engels2001a,
  author = {Gregor Engels AND Reiko Heckel AND Jochen K{\"u}ster},
  title = {Rule-Based Specification of Behavioral Consistency Based on the UML Meta-model},
  booktitle = {Proceedings of the conference on The Unified Modeling Language, Modeling Languages, Concepts, and Tools (UML 2001), Toronto (Canada)},
  year = {2001},
  editor = {M. Gogolla, C. Kobryn},
  pages = {272--287},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  month = {October},
  abstract = {Object-oriented modeling favors the modeling of object behavior from different viewpoints and at different levels of abstraction. This gives rise to consistency problems between overlapping or semantically related submodels.The absence of a formal semantics for the UML and the numerous ways of employing the language within the development process lead to a number of dierent consistency notions. Therefore, general meta-level techniques are required for specifying, analyzing, and communicating consistency constraints. In this paper, we discuss theissue of consistency of behavioral models in the UML and present techniques for specifying and analyzing consistency. Using meta-model rules we transform elements of UML models into a semantic domain. Then, consistency constraints can by specified and validated using the language and the tools of the semantic domain. This general methodology is exemplified by the problem of protocol statechart inheritance.}
}

@inproceedings{Sauer2001,
  author = {Stefan Sauer AND Gregor Engels},
  title = {UML-based Behavior Specification of Interactive Multimedia Applications},
  booktitle = {Proceedings of the IEEE Symposia on Human Centric Computing Languages and Environments (HCC 2001), Stresa (Italy)},
  year = {2001},
  pages = {248--255},
  publisher = {IEEE Computer Society},
  address = {Washington, DC, USA},
  month = {September},
  note = {Best Paper Award Symposium on Visual/Multimedia Approaches to Programming and Software Engineering.}
}

@inproceedings{Hausmann2000,
  author = {Gregor Engels AND Jan Hendrik Hausmann AND Reiko Heckel AND Stefan Sauer},
  title = {Dynamic Meta-Modeling: A Graphical Approach to the Operational Semantics of Behavioral Diagrams in UML},
  booktitle = {Proceedings of the 3rd international conference on the Unified Modeling Language (UML 2000), York (UK)},
  year = {2000},
  editor = {A. Evans, S. Kent, B. Selic},
  pages = {323--337},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  note = {Third International Conference},
  abstract = {In this paper, dynamic meta modeling is proposed as a new approach to the operational semantics of behavioral UML diagrams. The dynamic meta model extends the well-known static meta model by a speci.cation of the system’s dynamics by means of collaboration diagrams. In this way, it is possible to de.ne the behavior of UML diagrams within UML.The conceptual idea is inherited from Plotkin’s structured operational semantics (SOS) paradigm, a style of semantics speci.cation for concurrent programming languages and process calculi: Collaboration diagrams are used as deduction rules to specify a goal-oriented interpreter for the language. The approach is exemplified using a fragment of UML statechart and object diagrams.Formally, collaboration diagrams are interpreted as graph transformation rules. In this way, dynamic UML semantics can be both mathematically rigorous so as to enable formal specifications and proofs and, due to the use of UML notation, understandable without prior knowledge of heavy mathematic machinery. Thus, it can be used as a reference by tool developers, teachers, and advanced users.}
}

@inproceedings{Engels01,
  author = {Gregor Engels AND Reiko Heckel},
  title = {Graph Transformation as a Conceptual and Formal Framework for System Modeling and Model Evolution},
  booktitle = {Proceedings of the 27th International Colloquium on Automata, Languages and Programming (ICALP 2000), Geneva (Switzerland)},
  year = {2000},
  pages = {127-150},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  month = {July}
}

@inproceedings{Engels2000e,
  author = {Gregor Engels AND Luuk Groenewegen},
  title = {Object-Oriented Modeling - A Roadmap},
  booktitle = {Proceedings of the Conference on The Future of Software Engineering - Special Track at 22nd International Conference on Software Engineering (ICSE 2000), Limerick (Ireland)},
  year = {2000},
  editor = {A. Finkelstein},
  pages = {103--116},
  publisher = {ACM Press},
  address = {New York, NY, USA},
  month = {June },
  abstract = {Object-oriented modeling has become the de-facto standard in the early phases of a software development process during the last decade. The current state-of-the-art is dominated by the existence of the Unified Modeling Language (UML), the development of which has been initiated and pushed by industry.This paper presents a list of requirements for an ideal object-oriented modeling language and compares it with the achievements of UML and other object-oriented modeling approaches. This forms the base for the discussion of a roadmap for object-oriented modeling, which is structured according to a classification scheme of six different themes, which are language-, model- orprocess-related, respectively.}
}

@inproceedings{Engels2000c,
  author = {Gregor Engels AND Reiko Heckel AND Stefan Sauer},
  title = {UML - A Universal Modeling Language?},
  booktitle = {Proceedings of the 21st International Conference on Application and Theory of Petri Nets (ICATPN 2000), Aarhus (Denmark)},
  year = {2000},
  editor = {M. Nielsen, D. Simpson},
  pages = {24--38},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  month = {June},
  abstract = {Abstract. The Unified Modeling Language (UML) is the de facto industrial standard of an object-oriented modeling language. It consists of several sublanguages which are suited to model structural and behavioral aspects of a software system. The UML was developed as a general-purpose language together with intrinsic features to extend the UML towards problem domain-specific profiles. The paper illustrates the language features of the UML and its adaptation mechanisms. As a conclusion, we show that the UML or an appropriate, to be defined core UML, respectively, may serve as a universal base of an object-oriented modeling language. But this core has to be adapted according to problem domain-specific requirements to yield an expressive and intuitive modeling language for a certain problem domain.}
}

@inproceedings{Sauer1999a,
  author = {Stefan Sauer AND Gregor Engels},
  title = {Extending UML for Modeling of Multimedia Applications},
  booktitle = {Proceedings of the IEEE Symposium on Visual Languages (VL 1999), Tokyo (Japan)},
  year = {1999},
  editor = {M. Hirakawa, P. Mussio},
  pages = {80--87},
  publisher = {IEEE Computer Society},
  address = {Tokyo, Japan},
  abstract = {An analysis of how visual modeling of structure and dynamic behavior of a multimedia application differs from modeling conventional software yields that aspects of the graphical user interface and time-dynamic behavior ought to be integral parts of a coherent multimedia application model. In this sense, we extend the model-view-controller paradigm towards multimedia.As a result, we present OMMMA-L, a visual Language for the Object-Oriented Modeling of MultiMedia Applications that is based on the Unified Modeling Language (UML). The structural and behavioral diagram types of UML have been analyzed and are adapted and extended according to multimedia application characteristics.A presentation diagram is introduced and integrated to adequately describe the visual presentation. In addition to explaining the different diagram types, we also give pragmatic guidelines on how to deploy and combine the various diagrams.}
}

@inproceedings{Engels1999c,
  author = {Gregor Engels AND Ralph Depke AND Christoph Borowski},
  title = {Konzeption und objektorientierte Realisierung einer internet-basierten Datenbankanwendung},
  booktitle = {Kolloquium Software-Entwicklung - Methoden, Werkzeuge, Erfahrungen},
  year = {1999},
  editor = {H. J. Scheibl},
  pages = {531--540},
  publisher = {Technische Akademie Esslingen},
  address = {Ostfildern},
  month = {September},
  abstract = {Today e-commerce applications use web browsers as an uniform user interface and they rely on databases as datasources. Different technologies exist for database access: common gateway interface (CGI), Java and its databaseinterface java database connectivity (JDBC), proprietary approaches of database vendors, etc. We present criteria forthe selection of an appropriate solution and we successivly apply them in our application development process.Throughout the development process of internet based database applications object oriented techniques can be used.The unified modeling language (UML) is used for requirement analysis and design of the application and theimplementation proceeds with the programming language Java. The transition from the object oriented modelinglanguage UML to the object oriented programming language Java succeeds smoothly. We report on our experience withthe modeling tool Rational Rose 98 of Rational, Inc. We use Java and JDBC to implement a seminar reservation systemthat can be regarded as a small e-commerce application.}
}

@inproceedings{EngelsHSW1999,
  author = {Gregor Engels AND Roland H{\"u}cking AND Stefan Sauer AND Annika Wagner},
  title = {UML Collaboration Diagrams and Their Transformation to Java},
  booktitle = {Proceddings of The Unified Modeling Language: Beyond the Standard, Second International Conference (UML 99), Fort Collins, Colorado, USA},
  year = {1999},
  editor = {R. France, B. Rumpe},
  pages = {473--488},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  month = {October}
}

@inproceedings{Depke1998,
  author = {Ralph Depke AND Gregor Engels AND Katharina Mehner AND Stefan Sauer AND Annika Wagner},
  title = {Ein Ansatz zur Verbesserung des Entwicklungsprozesses von Multimedia-Anwendungen},
  booktitle = {Proceedings of the GI-Fachtagung on Softwaretechnik (1998), Paderborn (Germany)},
  year = {1998},
  pages = {12--19},
  publisher = {GI},
  month = {September }
}

@inproceedings{Engels97,
  author = {Gregor Engels AND Reiko Heckel AND Gabriele Taentzer AND Hartmut Ehrig},
  title = {A View-Oriented Approach to System Modelling Using Graph Transformations},
  booktitle = {Proceedings European Software Engineering Conference (ESEC 1997), Z{\"u}rich (Switzerland)},
  year = {1997},
  editor = {M. Jazayeri, H. Schauer},
  pages = {327--343},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  abstract = {The idea of a combined reference model- and view-based specification approach has been proposed recently in the software engineering community. In this paper we present a specification technique based on graph transformations which supports such a development approach. The use of graphs and graph transformations supports an intuitive understanding and an integration of static and dynamic aspects on a well-defined semantical base. On this background, formal notions of view and view relation are developed and the behaviour of views is described by a loose semantics. We define a construction for automatic view integration which assumes that the dependencies between different views are described by a reference model. The views and the reference model are kept consistent manually, which is the task of a model manager. All concepts and results are illustrated at the well-known example of a banking system.}
}

@inproceedings{EEH+96,
  author = {Gregor Engels AND Hartmut Ehrig AND Reiko Heckel AND Gabriele Taentzer AND Andrea Corradini},
  title = {A View-Based Approach to System Modelling},
  booktitle = {Report on Dagstuhl-Seminar 9637 on Graph Transformations in Computer Science},
  year = {1996},
  editor = {H. Ehrig, U. Montanari, G. Rozenberg, H.-J. Schneider},
  pages = {11},
  publisher = {Technical University of Berlin},
  month = {September},
  abstract = {In order to manage the complexity of large system specifications, they have to be decomposed into subspecifications. Each subspecification describes a certain part of the system. This might be a certain aspect, like the data, dynamic, or functional aspect, as it is known from object-oriented modelling techniques. Or it might be a certain view onto the system, as it is known from database modelling techniques. The talk motivates the usage of views in graph grammarbased specifications. First, the usage of typed graph grammars inherently ensures an integration of the data and the functional aspect within a view. Second, it is explained that it is not appropriate in case of views to have a fixed semantics.The standard fixed semantics, i.e. a graph transformation system, has to be relaxed to a loose semantics, i.e. a graph transition system. This reflects the idea that a view models only a part of the complete system. Other views may overlap a view with respect to data or functionality. A complete system specification is yielded by exploiting the approach of cooperative parallel composition of graph grammars (see talk by Leila Ribeiro).}
}

@inproceedings{Bunje1996,
  author = {Tineke de Bunje AND Gregor Engels AND Luuk Groenewegen AND Aart Matsinger AND Martin Rijnbeek},
  title = {Industrial maintenance modelled in SOCCA: an experience report},
  booktitle = {Proceedings of the Fourth International Conference on the Software Process (ICSP 1996), Brighton (UK)},
  year = {1996},
  pages = {13--26},
  publisher = {IEEE Computer Society},
  address = {Washington, DC, USA},
  abstract = {A large industrial process, software maintenance, has been modelled by using the process modelling language SOCCA. The paper reports about the experiences with this trial. In particular, feasibility, expressiveness, quality and the overall benefits of a formal SOCCA model are discussed and compared to the formerly existing informal process description. In order to illustrate the results, a well chosen process model fragment from the larger model is outlined in detail. It addresses in particular the human-intensive cooperation within the process and shows the seamless combination of technical components and human agent components in the SOCCA model. The main conclusions from this trial are that formal SOCCA models are suited to model realistic industrial processes and that due to an intrinsic modular structure of a SOCCA model, even huge models remain reasonably readable and understandable}
}

@inproceedings{EngelsGK1996a,
  author = {Gregor Engels AND Luuk Groenewegen AND Gerti Kappel},
  title = {Object-oriented specification of coordinated collaboration},
  booktitle = {Proceedings of IFIP World Conference on IT Tools (1996), Canberra (Australia)},
  year = {1996},
  editor = {N. Terashima, Ed. Altman},
  pages = {437--452},
  publisher = {Chapman & Hall},
  month = {September },
  abstract = {Object-oriented specification mechanisms have become famous for modelling structure and behaviour together in terms of autonomous objects communicating via message passing. However, whereas most object-oriented specification methods are strong in modelling the local behaviour of single objects, they fall short on modelling the coordinated behaviour and collaboration of several objects together The aim of this paper is to contribute to fill this gap. The paper reports on concepts, language constructs, and experiences with three collaboration formalisms in the area of object-oriented specifications.}
}

@inproceedings{Ehrig1996a,
  author = {Hartmut Ehrig AND Reiko Heckel AND Julia Padberg AND Gabriele Taentzer AND Uwe Wolter AND Andrea Corradini AND Gregor Engels},
  title = {Synchronization of Views and Loose Semantics of Typed Graph Productions},
  booktitle = {Report on the Dagstuhl-Seminar 9637 on Graph Transformations in Computer Science},
  year = {1996},
  pages = {11--12},
  publisher = {Technical University of Berlin},
  month = {September},
  abstract = {The concept of views is used on two levels. First, so-called design views are developed for structuring specifications, that is, a system is modeled according to different views (e.g., representing the needs of different kinds of users) which have to be synchronized afterwards in order to build the whole system. Views can be specified by means of typed graph transformation systems, where the type graph determines the visible types and the productions describe the known operations of that view. The synchronization of views is done by the construction of cooperative parallel composition of graph transformation systems, developed by Leila Ribeiro and presented at the same seminar.If the specification is complete, a view may describe an observation of the system in operation. In this case we speak of a user view. It turns out that the semantics of such a view cannot be described by computations (i.e., graph transformations), but just by observations of computations of the global system. Such observations of computations cannot be represented by graph transformations in the usual sense because a local view may lack operations (productions) of the global system, so that state changes may be observed that do not have a cause in the local view.Therefore, the notion of graph transition is introduced as loose semantics for productions, where the production specifies only a lower bound to the activities that are to happen during application. Contrastingly, in the classical doublepushout approach to graph rewriting, productions are interpreted as complete descriptions of the transformations to be performed.For typed graph transformation systems a transition sequence semantics is developed, comprising all finite and infinite sequences of transitions in a system.Moreover, this semantics is shown to be compositional w.r.t. the synchronization of views.}
}

@inproceedings{Engels1994b,
  author = {Gregor Engels AND Gerti Kappel},
  title = {Object-Oriented System Development: Will the New Approach Solve Old Problems?},
  booktitle = {Proceedings of the IFIP 13th World Computer Congress on Information Processing, Hamburg (Germany)},
  year = {1994},
  editor = {K. Duncan and K. Krueger},
  pages = {434--441},
  publisher = {Elsevier Science},
  month = {August },
  abstract = {Object-oriented system development is wideley recognized as improving productivity and reducing system maintenance costs. However, existing approaches have not sufficiently addressed the following three questions which are equally important to users and researchers. Firstly, what are the benefits of object-oriented system development compared to traditional approaches? Secondly, what are the essential features of an objectoriented life cycle model to fulfill the benefits of object-oriented development? And thirdly, what are the pitfalls of object-oriented development and how to cope with them? The paper investigates answers to all three questions in concert.}
}

@inproceedings{Ebert1994a,
  author = {J{\"u}rgen Ebert AND Gregor Engels},
  title = {Structural and Behavioural Views on OMT-Classes},
  booktitle = {Proceedings of the International Symposium on Object-Oriented Methodologies and Systems (ISOOMS 1994), Palermo (Italy)},
  year = {1994},
  editor = {E. Bertino, S. Urban},
  pages = {142-157},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  abstract = {Object-oriented specification languages provide means to specify the static structure, as well as the allowed dynamic behaviour of objects. Here, the dynamic behaviour is usually described by giving the methods and a state transition diagram which defines the allowed sequences of methods on objects of a certain class.Specialized classes are defined using the inheritance relationship. In order to enable reusability while guaranteeing type substitutability, subclass specifications have to be compatible with respect to static and dynamic aspects with their corresponding superclass specifications.Classes have to provide a large shopping list of operations to satisfy the needs of all possible users. The interests of specific users are often restricted to a subset of operations and thus to a restricted behaviour.This paper describes a formalization of class descriptions given by attributes, operations, as well as state transition diagrams. It defines compatibility between sub- and superclasses and introduces the notion of views in the sense of hiding parts of a class description. It turns out that a view has the same properties as a (virtual) superclass.}
}

@inproceedings{Engels94,
  author = {Gregor Engels AND Hartmut Ehrig},
  title = {Towards a Module Concept for Graph Transformation Systems: The Software Engineering Perspective},
  booktitle = {Proceedings Colloquium on Graph Transformation and its Application in Computer Science},
  year = {1994},
  editor = {G. Valiente Feruglio and F. Rossello Llompart},
  publisher = {Universitat de les Illes Balears, Departament de Ci},
  month = {M{\"a}rz}
}

@inproceedings{Engels1993,
  author = {Gregor Engels AND A.A. Verrijn-Stuart},
  title = {Integrationsaspekte bei verteilter Software-Entwicklung},
  booktitle = {Fortschritt-Berichte VDI},
  year = {1993},
  pages = {45--53},
  publisher = {VDI Verlag},
  month = {October}
}

@inproceedings{Koopman1992,
  author = {Pieter Koopman AND Luuk Groenewegen AND Gregor Engels},
  title = {Functional Description of Parallel Processes},
  booktitle = {Proceedings of the conference SION Computing Science in the Netherlands (CSN '92), The Netherlands},
  year = {1992},
  editor = {J.L.G. Dietz},
  pages = {156--167},
  note = {SION}
}

@inproceedings{Hohenstein1990,
  author = {Uwe Hohenstein AND Gregor Engels},
  title = {Formal Semantics of an Entity-Relationship Query Language},
  booktitle = {Proceedings of the 9th International Conference on Entity-Relationship Approach (ER 90), Lausanne, Switzerland},
  year = {1990},
  editor = {H. Kangassalo},
  pages = {177--188},
  publisher = {ER Institute},
  month = {October}
}

@inproceedings{Engels1989a,
  author = {Gregor Engels},
  title = {CADDY-O: Syntaxgest{\"u}tztes, graphisches Entwerfen konzeptioneller Datenbankschemata},
  booktitle = {Tagungsband GI-Fachtagung "Interaktive Schnittstellen f{\"u}r Informationssysteme", TU Clausthal, Notizen zu Interaktive Systeme},
  year = {1989},
  editor = {A. Heuer, I. Kupka},
  pages = {1-16},
  month = {November}
}

@inproceedings{Engels1989b,
  author = {Gregor Engels AND Uwe Hohenstein AND Klaus H{\"u}lsmann AND Perdita L{\"o}hr-Richter AND Hans-Dietrich Ehrich},
  title = {CADDY: Computer-Aided Design of Non-Standard Databases},
  booktitle = {Proceedings of the International Conference on System Development Environments & Factories, Berlin, Germany},
  year = {1989},
  editor = {N. Madhavji, W. Sch{\"a}fer, H. Weber},
  publisher = {Pitman Publishing},
  address = {Berlin},
  month = {May}
}

@inproceedings{Ebert1989,
  author = {J{\"u}rgen Ebert AND Gregor Engels},
  title = {Konzepte einer Software-Architektur-Beschreibungssprache},
  booktitle = {Software-Entwicklung: Konzepte, Erfahrungen, Perspektiven, Fachtagung, 1989, Marburg (Germany)},
  year = {1989},
  editor = {W.-M. Lippe},
  pages = {238--250},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  month = {June}
}

@inproceedings{Engels1988,
  author = {Gregor Engels AND Thorsten Janning AND Wilhelm Sch{\"a}fer},
  title = {A Highly Integrated Tool Set for Program Development Support},
  booktitle = {Proceedings of the conference on ACM SIGSMALL/PC symposium on ACTES (SIGSMALL 1988), Cannes (France)},
  year = {1988},
  pages = {1--10},
  publisher = {ACM Press},
  address = {New York, NY, USA},
  note = {SIGSMALL '88: Proceedings of the 1988 ACM SIGSMALL/PC symposium on ACTES},
  abstract = {This paper describes the design of the integrated user interface of the software development environment IPSEN (Integrated Programming Support Environment). We explain the characteristic features of the IPSEN user interface, namely the structured layout of the screen, the command-driven tool activation, and especially the highly integrated use of the IPSEN tool set. We demonstrate those features by taking a sample set of tools of the IPSEN environment. That tool set supports all the programming-in-the-small activities within IPSEN. Finally, we sketch the realization of two prototypes running on an IBM-AT and a net of SUN workstations.}
}

@inproceedings{EngelsHNSE1988a,
  author = {Gregor Engels AND Uwe Hohenstein AND Leonore Neugebauer AND Gunter Saake AND Hans-Dietrich Ehrich},
  title = {Konzeption einer integrierten Datenbank-Entwurfsumgebung},
  booktitle = {Proceedings of DBTA/SI Data Dictionaries und Entwicklungswerkzeuge f{\"u}r Datenbank-Anwendungen, Z{\"u}rich, Switzerland},
  year = {1988},
  editor = {F. Oertly},
  pages = {151--157},
  publisher = {Verlag der Fachvereine an den Schweiz. Hochschulen und Techniken}
}

@inproceedings{Engels1987,
  author = {Gregor Engels AND Andy Sch{\"u}rr},
  title = {A Hybrid Interpreter in a Software Development Environment},
  booktitle = {Proceedings of the 1st European Software Engineering Conference (ESEC '87), Strasbourg (France)},
  year = {1987},
  editor = {H.K. Nichols, D. Simpson},
  pages = {80--88},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  abstract = {This paper describes the realization of an execution tool for Modula-2 modules which ispart of an integrated tool set in a software development environment termed IPSEN (IncrementalProgramming Support Environment). In this environment, all software documents, e.g.Modula-2 modules, are manipulated by syntax-directed editors and are represented internallyby attributed graphs. The execution of Modula-2 modules is done by two cooperating interpreters.The first one is a graph interpreter which traverses the internal graph from statementto statement. These statements are translated into a low-level, more efficiently executable objectcode and interpreted by a second interpreter. This concept of a hybrid interpreter allowsthe realization of an execution tool which offers a lot of runtime support features to the user.}
}

@inproceedings{EngelsNS1987a,
  author = {Gregor Engels AND Manfred Nagl AND Wilhelm Sch{\"a}fer},
  title = {On the Structure of Structure-Oriented Editors for Different Applications},
  booktitle = {Proceedings of the ACM SIGSOFT/SIGPLAN Software Engineering Symposium on Practical Software Development Environments, Palo Alto, USA},
  year = {1987},
  editor = {P. Henderson},
  pages = {190--198},
  publisher = {ACM SIGPLAN Notices},
  month = {January}
}

@inproceedings{EngelsLNS1986b,
  author = {Gregor Engels AND Claus Lewerentz AND Manfred Nagl AND Wilhelm Sch{\"a}fer},
  title = {On the Structure of an Incremental and Integrated Software Development Environment},
  booktitle = {Proceedings of the 19th Hawaii International Conference on System Sciences, Hawaii, USA},
  year = {1986},
  pages = {585--597}
}

@inproceedings{Engels1985a,
  author = {Gregor Engels AND Wilhelm Sch{\"a}fer},
  title = {Graph Grammar Engineering: A Method Used for the Development of an Integrated Programming Support Environment},
  booktitle = {Proceedings of the International Joint Conference on Theory and Practiceof Software Development (TAPSOFT 1985), Berlin (Germany)},
  year = {1985},
  editor = {H. Ehrig, C. Floyd, M. Nivat, J. W. Thatcher},
  pages = {179--193},
  publisher = {Springer},
  address = {Berlin/Heidelberg},
  abstract = {We introduce a method to specify the functional behaviour of software tools in an incremental and integrated software development environment. This specification method is based on graph grammars. It is an adequate method to specify the behaviour of all software systems using graphs as internal data structures. We show that a specification can be developed systematically by which the adaptability of the environment is increased towards modification of tools or extension by new tools. Furthermore, guidelines for the implementation can directly be derived from this specification.}
}

@inproceedings{EngelsS1985m,
  author = {Gregor Engels AND Wilhelm Sch{\"a}fer},
  title = {The Design of an Adaptive and Portable Programming Support Environment},
  booktitle = {Proceedings of the International Computing Symposium, Amsterdam (The Netherlands)},
  year = {1985},
  editor = {G. Valle, G. Bucci},
  address = {Florenz}
}

@inproceedings{Pletat1982,
  author = {Udo Pletat AND Gregor Engels AND Hans-Dietrich Ehrich},
  title = {An Operational Approach to Conditional Algebraic Specifications},
  booktitle = {Proceedings of the 7eme Colloque sur les Arbres en Algebre et en Programmation, Lille (France)},
  year = {1982},
  editor = {H.J. Schneider, H. G{\"o}ttler},
  pages = {254--270},
  month = {March },
  abstract = {We suppose to give conditional specifications of abstract data types hierarchically. Considering algebraic specifications from an operational point of view this approach enables us to present simple syntactic criteria for the Church-Rosser property, which implies the welldefinedness of the operational semantics of a conditional specification. Furthermore, these criteria are sufficient for the termination of the full substitution reduction strategy. }
}

@inproceedings{Engels1982,
  author = {Gregor Engels AND Wilhelm Sch{\"a}fer},
  title = {Specification of a Programming Support Environment by Graph Grammars},
  booktitle = {Proceedings of the conference on Graphtheoretic Concepts in Computer Science (WG`82), M{\"u}nchen (Germany)},
  year = {1982},
  editor = {H.J. Schneider and H. G{\"o}ttler},
  pages = {47--62},
  publisher = {Hanser},
  address = {M{\"u}nchen/Leipzig}
}

@inproceedings{SEH10,
  author = {Frank Salger AND Gregor Engels AND Alexander Hofmann},
  title = {Assessments in Global Software Development: A Tailorable Framework for Industrial Projects},
  booktitle = {Proceedings ACM/IEEE 32nd International Conference on Software Engineering, Software Engineering in Practice Track, May 2010, Cape Town, South Africa (to appear)},
  editor = {W. Visser, I. Kr{\"u}ger}
}

@misc{EngArchi08,
  author = {Arndt Bode AND Manfred Broy AND Uwe Dumslaff AND Gregor Engels},
  title = {Architektur & Management im Großen meistern},
  howpublished = {Editorial of "Informatik-Spektrum" (special issue "Management großer Systeme"), vol. 31, no. 6. Springer (Berlin/Heidelberg)},
  year = {2008}
}

@misc{Doberkat,
  author = {Ernst-Erich Doberkat AND Gregor Engels AND Jan Hendrik Hausmann AND Marc Lohmann AND Christof Veltmann},
  title = {Anforderungen an eine eLearning-Plattform -Innovation und Integration},
  howpublished = {Study for the Ministry of Science and Research, Northrhine-Westfalia, Germany},
  month = {April},
  year = {2002}
}

@misc{Engels1994c,
  author = {Gregor Engels},
  title = {Coordination Constraints (Abstract)},
  howpublished = {In H.-D. Ehrich, G. Engels, J. Paredaens, P. Wegner (eds.): Fundamentals of Object-Oriented Languages, Systems, and Methods- Dagstuhl-Seminar-Report 95},
  month = {August},
  year = {1994},
  abstract = {Nowadays object-oriented analysis and design methods propose to split the specification of a system into several parts, where each part describes a certain perspective. We follow this line and present the object-oirented specification language SOCCA (Specification of Coordinated and Cooperative Activities). A SOCCA specification consists of* a class diagram to describe the structural part of objects and their interrelations with other objects,* state transition diagrams to describe the external behavior ("life cycle") of objects,* an interaction diagram to describe the "uses" relationschip between classes, and* (once more) state trasition diagrams to describe the internal behavior ("realization") of operations.In addition to most of the existing appproaches, we also model the coordination of object behavior explicitly. This is done by splitting the internal behavior description into subdiagrams and by controlling the transition from one subbehavior to another by coordination constraints added to the external behavior description of objects. }
}

@misc{Engels1992d,
  author = {Gregor Engels},
  title = {Graphs as Central Data Structures in a Database Design Environment (Abstract)},
  howpublished = {In P. Klint, T. Reps, G. Snelting (eds.): Programming Environments. Dagstuhl-Seminar-Report 34},
  month = {March},
  year = {1992},
  abstract = {The talk illustrates that graphs are a well-suited data structure to be used for the modelling, i.e., external representation, as well as for the internal representation of database schemas.We present the database design environment CADDY (Computer-Aided conceptual Design of non-traditional Databases) which offers an integrated tool set for editing, and prototyping a conceptual database schema. The theoretical background is given by a semantically well-defined data model which enables the specification of the static structure of an appliction area by an Extended Entity-Relationship diagram and the specification of the dynamic behaviour by temporal integrity constraints and extended data flow graphs. The tool set of CADDY comprises language-sensitive editors for all these specification paradigms and prototyping tools like a query interpreter or a graphical database browser to join experiences with partly developed coneptual database schemata.All developed documents within CADDY are internally represented by attributed abstract syntax graphs. These are extensions of abstract syntax trees, where in addition to context-free interrelations also context-sensitive interrelations are expressed by nodes and edges. The classes of these syntax graphs are specified by an operational specification approach which is based on programmed graph representation systems. These graph grammar specifications serve as guideline for an efficient implementation of all CADDY-tools.}
}

@misc{Engels1992b,
  author = {Gregor Engels},
  title = {Schakelschema's voor Softwaresystemen},
  howpublished = {Reprint Inaugurale Rede, Rijksuniversit{\"a}t Leiden},
  month = {September},
  year = {1992}
}

@phdthesis{Engels1986,
  author = {Gregor Engels},
  title = {Graphen als zentrale Datenstrukturen in einer Software-Entwicklungsumgebung},
  school = {University of Osnabr{\"u}ck},
  year = {1986},
  note = {VDI-Fortschritt-Berichte Nr. 62, Dsseldorf: VDI-Verlag 1986>Fortschritt-Berichte VDI., Reihe 10,, Angewandte Informatik ;, Nr. 62}
}

@proceedings{ELS09,
  title = {Software Engineering 2010 - Proceedings},
  year = {2010},
  publisher = {K{\"o}llen Verlag (Bonn)}
}

@proceedings{ERMS09,
  title = {Proceedings of Design for Future - 1. Workshop des GI-Arbeitskreises "Langlebige Softwaresysteme (L2S2)"},
  year = {2009},
  editor = {Gregor Engels, Ralf Reussner, Christof Momm, Stefan Sauer},
  publisher = {Karlsruhe},
  note = {15.-16. Oktober 2009FZI Forschungszentrum Informatik, Karlsruhe}
}

@proceedings{Engels2007b,
  title = {Proceedings of the 10th International Conference on Model Driven Engineering Languages and Systems (MoDELS 2007), Nashville, TN (USA)},
  year = {2007},
  editor = {Gregor Engels, Bill Opdyke, Douglas C. Schmidt, Frank Weil},
  publisher = {Springer}
}

@proceedings{Engels2004,
  title = {Modeling and Development of Multimedia Systems},
  year = {2004},
  editor = {Gregor Engels, Stefan Sauer},
  publisher = {World Scientific},
  month = {December},
  note = {(guest editors)}
}

@proceedings{Engels2004a,
  title = {Proceedings of "DeLFI 2004: Die 2. e-Learning Fachtagung Informatik", Paderborn (Germany)},
  year = {2004},
  editor = {Gregor Engels, Silke Seehusen},
  publisher = {Gesellschaft f{\"u}r Informatik},
  note = {6.-8. September 2004 in Paderborn}
}

@proceedings{Ehrig2004,
  title = {Proceedings of the 2nd International Conference on Graph Transformations (ICGT 2004), Rome (Italy)},
  year = {2004},
  editor = {Hartmut Ehrig, Gregor Engels, Francesco Parisi-Presicce, Grzegorz Rozenberg},
  publisher = {Springer},
  month = {September}
}

@proceedings{Engels01b,
  title = {Modellierung 2001},
  year = {2001},
  editor = {Gregor Engels, Andreas Oberweis, Albert Z{\"u}ndorf},
  publisher = {K{\"o}llen-Verlag},
  month = {March},
  abstract = {Die seit 1998 bestehende Workshop-Reihe Modellierung hat es sich zum Ziel gesetzt, ein Forum f{\"u}r den interdisziplin{\"a}ren Austausch von Ans{\"a}tzen und Erfahrun gen im Bereich der Modellierung zu bieten. Da in den einzelnen Fachdisziplinen unterschiedliche Traditionen und Terminologien in Bezug auf Modellierung bestehen, sind solche disziplin{\"u}bergreifenden Arbeitstreffen besonders n{\"u}tzlich und fruchtbar.Modellierung 2001 bietet daher Wissenschaftlern und Praktikern erneut die Gelegenheit, Gemeinsamkeiten, Defizite und Unterschiede in den verwendeten Mo dellierungsans{\"a}tzen herauszuarbeiten und gegenseitigen Erfahrungsaustausch zu pflegen. Um diesen Anspruch zu unterstreichen, wird es auch w{\"a}hrend der Modellierung 2001 neben den Vortr{\"a}gen viel Raum f{\"u}r Diskussionen geben. }
}

@proceedings{Ehrig00,
  title = {Special Issue: Selected Papers of GRATRA 2000},
  year = {2000},
  editor = {Hartmut Ehrig, Gregor Engels, Hans-J{\"o}rg Kreowski, Gabriele Taentzer},
  publisher = {Elsevier Science}
}

@proceedings{Engels99-2,
  title = {Informatik '99: Informatik {\"u}berwindet Grenzen. Tagungsband der 29. Jahrestagung der Gesellschaft f{\"u}r Informatik, Paderborn (Germany)},
  year = {1999},
  editor = {Gregor Engels, Kurt Beiersd{\"o}rfer, Wilhelm Sch{\"a}fer},
  publisher = {Springer},
  month = {October}
}

@proceedings{Engels00-2,
  title = {6th International Workshop on Theory and Applications of Graph Transformations (TAGT '98), Paderborn, Selected Papers},
  year = {1998},
  editor = {Gregor Engels, Hartmut Ehrig, Hans-J{\"o}rg Kreowski, Grzegorz Rozenberg},
  publisher = {Springer},
  month = {November },
  abstract = {This book constitutes the thoroughly refereed post-workshop proceedings of the 6th International Workshop on Theory and Applications of Graph Transformations held in Paderborn, Germany, in November 1998. The 33 revised full papers presented in the book were carefully reviewed and selected from a total of 55 papers presented at the meeting. The book addresses all current aspects in the area. The papers are organized in sections on graph languages, graph theory, categorical approaches, concurrency and distribution, artificial intelligence, visual languages, specification concepts, modularity and refinement, and software engineering. }
}

@proceedings{Engels98,
  title = {Semi-Formal and Formal Specification Techniques},
  year = {1998},
  editor = {Gregor Engels, Hartmut Ehrig, Fernando Orejas, Martin Wirsing},
  publisher = {Schloss Dagstuhl, Leibniz Center for Informatics},
  month = {Juli},
  abstract = {During the last 20 years several different formal and semi-formal specification techniques have been successfully developed and used. Applications comprise the specification of simple programs, data types and processes as well as complex hardware and software systems. The variety of specification techniques ranges from formal set theoretical, algebraic, and logic approaches for specifying sequential systems and from Petri-nets, process algebras, automata, and graph grammars for specifying concurrent and distributed behaviors to semi-formal software engineering methods for developing complex systems.Formal and semi-formal approaches have their advantages and disadvantages: the informal diagrammatic methods are easier to understand and to apply but they can be ambiguous. Due to the different nature of the employed diagrams and descriptions it is often difficult to get a comprehensive view of all functional and dynamic properties. On the other hand, the formal approaches are more difficult to learn and require mathematical training. But they provide mathematical rigor for analysis and prototyping of designs. Verification is possible only with formal techniques.Since a few years many researchers and research groups are putting more and more effort in closing this gap by integrating semi-formal and formal specification techniques. Their studies and experiences show the added value of combining semi-formal and formal techniques and at the same time open a whole range of new problems and questions which cannot be asked when studying formalisms in isolation.In this seminar more than 40 scientists came together in 28 talks and two panel discussions to study possibilities and solutions for integrating and validating different formal and semi-formal specification techniques. Similarities and differences of formal and semi-formal specification formalisms as well as possibilities for combining such techniques were discussed. Most talks of this seminar analysed, compared, or integrated at least two such methods.On behalf of all participants the organizers would like to thank the staff of Schloss Dagstuhl for providing an excellent environment to the conference. The support of the TMR programme of the European Community is gratefully acknowledged. Due to this programme it was possible to fund the participation of several young researchers and of three key note speakers. }
}

@proceedings{Engels97-2,
  title = {Themenheft: Softwaretechnik},
  year = {1997},
  editor = {Gregor Engels},
  publisher = {Springer},
  month = {December },
  note = {(guest editor)}
}

@proceedings{Engels96,
  title = {Special Issue on Graph Transformations},
  year = {1996},
  editor = {Andrzej Skowron, Gregor Engels, Hartmut Ehrig, Grzegorz Rozenberg},
  publisher = {IOS Press},
  month = {June}
}

@proceedings{Ehrich94,
  title = {Fundamentals of Object-Oriented Languages, Systems, and Methods},
  year = {1994},
  editor = {Hans-Dietrich Ehrich, Gregor Engels, Jan Paredaens, Peter Wegner},
  publisher = {Schloss Dagstuhl, Leibniz Center for Informatics},
  month = {August},
  abstract = {During the last decades there has been progress within the object-oriented community in agreeing on what object- orientedness means. The role of object identity, specialization, inheritance, and dynamic binding have been examined. However, a careful look at articles written by people with a theory, programming language, database, and software engineering background shows that the semantical understanding of the same features still differs considerably. A well-known example is the feature of inheritance, which has quite a different meaning for persons from the database comunity with a semantic data model background and persons form the programming language community with a compiling technique background This observation also applies to the literaute on object-oriented software development methods. Here, object -oriented analysis and design methods are often heavily influenced by semantic data modelling consepts- An implemantion of an object-orinted design by an objeckt-oriented progamming language usually causes more difficulties than expected although the "same" object-oriente paradigm is used...}
}

@proceedings{Cuny96,
  title = {Graph Gramars and Their Application to Computer Science, 5th International Workshop (1994), Selected Papers},
  year = {1994},
  publisher = {Springer},
  month = {November},
  abstract = {This book contains a collection of 37 refereed full papers selected from the contributions presented at the 5th International Workshop on Graph Grammars and Their Applications to Computer Science, held in Williamsburg, Virginia, USA, in November 1994.The book covers the whole spectrum of methods and techniques for the investigation of the structure of graphs and graph transformations. The papers are divided into nine topical sections on rewriting techniques, specification and semantics, software engineering, algorithms and architectures, concurrency, graph languages, pattern and graphics, structure and logic of graphs, and biology.}
}

@proceedings{Ehrich1989,
  title = {Abstracts des Workshops "Grundlagen von Datenbanken", Volkse (Germany)},
  year = {1989},
  editor = {Hans-Dietrich Ehrich, Gregor Engels, Martin Gogolla, Gunter Saake},
  publisher = {Technische Universit{\"a}t Braunschweig}
}

@techreport{GerthTR10,
  author = {Christian Gerth AND Markus Luckey AND Jochen K{\"u}ster AND Gregor Engels},
  title = {Detection of Semantically Equivalent Fragments for Business Process Model Change Management},
  institution = {IBM Research - Zurich},
  year = {2010},
  type = {IBM Research Report},
  number = {3767},
  month = {February},
  abstract = {Modern business process modeling environments support distributed development by means of model version control, i.e., comparison and merging of two different model versions. This is a challenging task since most modeling languages support an almost arbitrary creation of process models. Thus, in multi-developer environments, process models or parts of them are often syntactically very different but semantically equivalent. Hence, the comparison of business process models must be performed on a semantic level rather then on a syntactic level. For the domain of business process modeling, this problem is yet unsolved.This paper describes an approach that allows the semantic comparison of different business process models using a normal form. For that purpose, the process models are fully automatically translated into process model terms and normalized using a term rewriting system. The resulting normal forms can be efficiently compared. Our approach enables the semantic comparison of business process models ignoring syntactic redundancies.}
}

@techreport{Lohmann2006b,
  author = {Marc Lohmann AND Jan-Peter Richter AND Gregor Engels AND Baris G{\"u}ldali AND Oliver Juwig AND Stefan Sauer},
  title = {Semantische Beschreibung von Enterprise Services – Eine industrielle Fallstudie},
  institution = {University of Paderborn, s-lab},
  year = {2006},
  type = {s-lab report},
  number = {1},
  month = {May},
  abstract = {Serviceorientierte Architekturen (SOA) erlauben eine schnelle und kosteneffiziente Bereitstellung unterschiedlicher Funktionalit{\"a}ten zur Unterst{\"u}tzung der Gesch{\"a}ftsprozesse eines Unternehmens. Dazu werden fachliche Funktionalit{\"a}ten in Form von Enterprise Services zur Verf{\"u}gung gestellt. Die hohe Zahl von Enterprise Services erfordert eine geeignete semantische Beschreibung zu deren effizienten Verwaltung. Zur semantischen Beschreibung von Enterprise Services sowie zur Formulierung von Suchanfragen ist an der Universit{\"a}t Paderborn die Methode der visuellen Kontrakte entwickelt worden. Dieser Bericht stellt die Ergebnisse einer industriellen Fallstudie zur Evaluation der praktischen Anwendbarkeit visueller Kontrakte im Kontext einer SOA vor.}
}

@techreport{EngelsKG2001d,
  author = {Gregor Engels AND Jochen K{\"u}ster AND Luuk Groenewegen},
  title = {On the Specification and Analysis of Protocols in UML-RT},
  institution = {University of Paderborn, Department of Computer Science},
  year = {2001},
  type = {Technical report},
  number = {01-221 },
  month = {January}
}

@techreport{Depke2000,
  author = {Ralph Depke AND Gregor Engels AND Jochen K{\"u}ster},
  title = {On the Integration of Roles in the UML},
  institution = {University of Paderborn, Department of Computer Science},
  year = {2000},
  type = {Technical report},
  number = {214},
  month = {August },
  abstract = {Conventionally, the state space and behavior of an object is determined when the object is created. Attributes and methods are not allowed to be attached to or retracted from an object during its lifetime. In other words, it is not feasible for an object to change its type dynamically. Furthermore, it is not possible to define several different views on an object allowing to exhibit a specific view to another object and hiding part of its features to a particular object. As a consequence, the concept of an object does not reflect appropriately real-world entities which may change their behavior and exhibit only part of their behavior towards another real-world entity. The concept of a role has been considered as an appropriate step forward to solving these kinds of problems. In this paper, we examine the concept of roles and elaborate a proposal for the integration of a clear concept of roles in the UML.}
}

@techreport{Engels1999f,
  author = {Gregor Engels AND Ray Dassen AND Luuk Groenewegen AND Ida G. Sprinkhuizen-Kuyper AND Pieter Koopman AND Pieter Jan t'Hoen},
  title = {A Formalisation of SOCCA using Z, part 1: The Type Level Concepts},
  institution = {Leiden Institute of Advanced Computer Science},
  year = {1999},
  type = {Technical report},
  number = {1999-03},
  abstract = {This document starts the formalisation of the modelling language of the SOCCA OO method in the formal specification language Z. It captures the `static' aspects of SOCCA, i.e. the meaning of SOCCA language elements at the type level, rather than `dynamic' aspects (dealing with the instance level (objects in execution)). It is restricted to core SOCCA; proposed extensions are not formalised.}
}

@techreport{Engels1999e,
  author = {Gregor Engels AND Pieter Jan t'Hoen AND Ray Dassen AND Luuk Groenewegen AND Ida G. Sprinkhuizen-Kuyper AND Pieter Koopman},
  title = {SOCCA Extended with UML like Packages},
  institution = {Leiden Institute of Advanced Computer Science},
  year = {1999},
  type = {Technical report},
  number = {99-06},
  month = {September}
}

@techreport{Engels1999a,
  author = {Gregor Engels AND Roland H{\"u}cking AND Stefan Sauer AND Annika Wagner},
  title = {UML Collaboration Diagrams and Their Transformation to Java},
  institution = {University of Paderborn, Department of Computer Science},
  year = {1999},
  type = {Technical report},
  number = {99-208},
  month = {June},
  note = {Extended version of UML'99. },
  abstract = {UML provides a variety of diagram types for specifying boththe structure and the behavior of a system. During the developmentprocess, models specied by use of these diagram types have to be transformedinto corresponding code. In the past, mainly class diagrams andstate diagrams have been considered for an automatic code generation.In this paper, we focus on collaboration diagrams. As an important prerequisitefor a consistent transformation into Java code, we rst providemethodical guidelines on how to deploy collaboration diagrams to modelfunctional behavior. This understanding yields a rened meta model andforms the base for the denition of a transformation algorithm. The automaticallygenerated Java code fragments build a substantial part ofthe functionality and prevent the loss of important information duringthe transition from a model to its implementation.}
}

@techreport{EngelsK1998,
  author = {Gregor Engels AND Silvia Kolmschlag},
  title = {Electronic Commerce Systeme als Anwendungsbeispiel f{\"u}r Evolutionstechniken},
  institution = {University of Paderborn, C-LAB},
  year = {1998},
  type = {C-LAB report},
  number = {06/98}
}

@techreport{Busatto1996,
  author = {Giorgio Busatto AND Gregor Engels},
  title = {Definition of an Encapsulated Hierarchical Graph Data Model: Static Aspects, Part 1.},
  institution = {Vakgroep Informatica, Rijksuniversiteit Leiden},
  year = {1996},
  type = {Technical report},
  number = {96-38},
  month = {December},
  abstract = {Graph grammars have been successfully used as a formalism for the specification of realistic problems but, as far as specification-in-the-large activities are concerned, they still have some deficiencies. In particular, most of them only support the use of flat graphs, whereas for certain applications hierarchical graphs would be a more suitable modelling tool. Furthermore, there is still the need for a graph grammar module concept that allows to split large specifications into smaller sub-specifications. We want to address this problem by applying object-oriented concepts to develop a hierarchical graph data model that supports a suitable module concept for graph grammars. In this paper, we present the first step in the definition of our encapsulated hierarchical graph (EHG) data model. We introduce the notion of EHG that supports complex nodes (i.e. nodes with an encapsulated graph as their content), edges, encapsulated graphs (i.e. graphs that support importing and exporting of nodes and edges), hierarchical structuring of complex nodes (through a node-subnode relationship), and appropriate conditions for exporting elements of a node along a hierarchy of nodes.}
}

@techreport{Andries1996a,
  author = {Marc Andries AND Gregor Engels AND Annegret Habel AND Berthold Hoffmann AND Hans-J{\"o}rg Kreowski AND Sabine Kuske AND Detlef Plump AND Andy Sch{\"u}rr AND Gabriele Taentzer},
  title = {Graph Transformation for Specification and Programming},
  institution = {University of Bremen, Department of Mathematics and Computer Science},
  year = {1996},
  type = {Technical report},
  number = {7/96},
  abstract = {The framework of graph transformation combines the potentials and advantages of both, graphs and rules, into a single computational paradigm. In this paper we survey recent developments in applying graph transformation as a rule-based framework for the specification and development of systems, languages, and tools. After presenting the basic features of graph transformation, we discuss a spectrum of applications including the evaluation of functional expressions, the specification of an interactive graphical tool, an example specification for abstract data types, and the definition of a visual database query language. The case studies indicate the need for a graph transformation language that provides suitable structuring principles and is independent of a particular graph transformation approach. To this end, we sketch the basic features of the new graph- and rule-centered language Grace, currently under development, that permits systematic and structured specification and programming based on graph transformation.}
}

@techreport{Engels1996c,
  author = {Gregor Engels AND Luuk Groenewegen AND Gerti Kappel},
  title = {Object-oriented Specification of Coordinated Collaboration},
  institution = {Vakgroep Informatica, Rijksuniversiteit Leiden},
  year = {1996},
  type = {Technical report},
  month = {August}
}

@techreport{Engels1995a,
  author = {Gregor Engels AND Andy Sch{\"u}rr},
  title = {Encapsulated Hierarchical Graphs, Graph Types, and Meta Types},
  institution = {Vakgroep Informatica, Rijksuniversiteit Leiden},
  year = {1995},
  type = {Technical report},
  number = {95-21},
  month = {July},
  abstract = {Currently existing graph grammar-based specification languages have serious problems with supporting any kind of "specification-in-the-large" activities. More precisely they have deficiences with respect to modeling hierarchical data structures or specifying meta activities like manipulation of graph schemata. Furthermore already proposed graph grammar module concepts are still too abstract to be useful in practice. Our contribution addresses these problems by introducing a new hierarchical graph data model with an infinite number of schema, meta-schema, etc. layers. It forms the base for a forthcoming concrete modular graph grammar specification language where in addition information hiding aspects like explicit export and import interfaces are expressible.}
}

@techreport{EbeEng1995,
  author = {J{\"u}rgen Ebert AND Gregor Engels},
  title = {Specialization of Object Life Cycle Definitions},
  institution = {University of Koblenz-Landau},
  year = {1995},
  type = {Fachbericht Informatik},
  number = {19/95},
  month = {December},
  note = {Koblenz},
  abstract = {Several object-oriented modeling approaches propose to describe the dynamic behaviour of objects by state transition diagrams. None of them provides precise rules or conditions for the interrelation between the behaviour description of classes and those of their subclasses. In this paper, we discuss this interrelation in detail. It turns out that one has to distinguish between the observable and the invocable behaviour of objects and that different compatibility requirements between the diagrams exist depending on the type of behaviour.}
}

@techreport{Ebert1994b,
  author = {J{\"u}rgen Ebert AND Gregor Engels},
  title = {Observable or Invocable Behaviour - You Have to Choose},
  institution = {Vakgroep Informatica, Rijksuniversiteit Leiden},
  year = {1994},
  type = {Technical report},
  number = {94-38},
  month = {December},
  abstract = {Several object-oriented modeling approaches propose to describe the dynamic behaviour of objects by state transition diagrams. None of them provide precise rules or conditions for the interrelation between the behaviour description of classes and those of their subclasses. In this paper, we discuss this interrelation in detail. It turns out that one has to distinguish between the observable and the invocable behaviour of objects and that different compatibility requirements between the diagrams exist depending on the type of behaviour.}
}

@techreport{Andries1993,
  author = {Marc Andries AND Gregor Engels},
  title = {A Hybrid Query Language for the Extended Entity Relationship Model},
  institution = {Vakgroep Informatica, Rijksuniversiteit Leiden},
  year = {1993},
  type = {Technical Report},
  number = {93-15},
  abstract = {We present the hybrid query language HQL/EER for an Extended Entity-Relationship model. As its main characteristic, this language allows a user to freely mix graphical and textual formulation of a query. We demonstrate the user-friendliness of this query language by means of examples, and show how syntax and semantics of this language are formally defined using programmed graph rewriting systems. Although we present the language in the context of the EER model, the concept of hybrid languages is applicable in the context of other database models as well. }
}

@techreport{Engels93,
  author = {Gregor Engels AND Grzegorz Rozenberg},
  title = {Abstracts COMPUGRAPH II Workshop},
  institution = {Vakgroep Informatica, Rijksuniversiteit Leiden},
  year = {1993},
  type = {Technical Report},
  number = {93-26},
  month = {September }
}

@techreport{Ehrig1993,
  author = {Hartmut Ehrig AND Gregor Engels},
  title = {Towards a Module Concept for Graph Transformation Systems},
  institution = {Vakgroep Informatica, Rijksuniversiteit Leiden},
  year = {1993},
  type = {Technical report},
  number = {93-34},
  month = {October}
}

@techreport{Engels1992e,
  author = {Gregor Engels},
  title = {Visual Specifications of Conceptual Database Schemata (Abstract)},
  institution = {Leiden University},
  year = {1992},
  type = {Dagstuhl-Seminar-Report: Foundation of Information Systems Specification and Design},
  month = {M{\"a}rz }
}

@techreport{Loehr-Richter1991,
  author = {Perdita L{\"o}hr-Richter AND Gregor Engels},
  title = {Incremental Design of Conceptual Database Schemata with CADDY},
  institution = {Vakgroep Informatica, Rijksuniversiteit Leiden},
  year = {1991},
  type = {Technical report},
  number = {91-23},
  month = {December}
}

@techreport{Engels1998,
  author = {Gregor Engels},
  title = {Benutzerschnittstelle und Architektur der integrierten Datenbankentwurfsumgebung CADDY (Kurzfassung)},
  institution = {TU Braunschweig},
  year = {1989},
  type = {Forschungsbericht},
  number = {89-02},
  month = {Mai}
}

@techreport{Ebert1988,
  author = {J{\"u}rgen Ebert AND Gregor Engels},
  title = {Ein Konzept zur Beschreibung von Software-Architekturen},
  institution = {EWH Koblenz},
  year = {1988},
  type = {Fachberichte Informatik},
  number = {11/88}
}

@techreport{Engels1981,
  author = {Gregor Engels AND Udo Pletat AND Hans-Dietrich Ehrich},
  title = {Handling Errors and Exceptions in the Algebraic Specifications of Data Types},
  institution = {University of Osnabr{\"u}ck},
  year = {1981},
  type = {Technical report},
  number = {OSM-I-3}
}

@techreport{Pletat1981,
  author = {Udo Pletat AND Gregor Engels AND Hans-Dietrich Ehrich},
  title = {Operational Semantics of Algebraic Specifications with Conditional Equations},
  institution = {University of Dortmund, Department of Computer Science},
  year = {1981},
  type = {Technical report},
  number = {118}
}

@booklet{Engels08-3,
  title = {Principles of Service-Oriented Architectures (SOA)},
  author = {Gregor Engels},
  howpublished = {Tutorial at the 30th International Conference on Software Engineering (ICSE '08), Leipzig (Germany)},
  month = {May},
  year = {2008},
  abstract = {Service-oriented architectures (SOA) are promoted as the final answer to the long standing demand to bridge the gap between business needs and IT-solutions. Like object-orientation has been advocated as the overall structuring principle in the 90s, service-orientation is nowadays discussed as the magic bullet to align business requirements with software applications.As it is typical for any hype approach, a commonly agreed understanding of the basic principles and notions for service-oriented concepts is still missing. This leads often to misunderstandings and communication problems in IT-projects and, thus, jeopardizes the success of migration projects where existing architectures are advanced towards service-oriented architectures.The tutorial aims at clarifying the understanding of basic principles, notions, languages as well as methods of a service-oriented approach. It lays the foundation for Tutorial T11, which will show how SOA is used in practice to achieve enterprise integration. All introduced concepts are related to existing knowledge on software architectures, architectural styles, and architecture frameworks. Presented methodical guidelines have been derived from successful industrial IT-projects and are part of Quasar Enterprise, the service-oriented development approach of sd&m AG, Munich (Germany).The tutorial is intended for industrial as well as academic people who are interested in a better understanding of basic principles and notions of service-oriented architectures, in order to judge benefits and risks of following a service-oriented approach.}
}

@booklet{Engels,
  title = {Object-Oriented System Development - From Analysis to Implementation},
  author = {Gregor Engels AND Gerti Kappel},
  howpublished = {Tutorials at the European Software Engineering Conference (ESEC '93), Garmisch-Partenkirchen (Germany), the International Conference on Database and Expert Systems Applications (DEXA '93), Prague (Czech Republic), and the International Conference on Data Engineering (ICDE '94), Houston, TX (USA)},
  year = {1993},
  abstract = {Object-oriented system development is widely recognized as improvingproductivity and reducing system maintenance costs.Since the late eighties an ever growing number of methods covering (part of)object-oriented analysis, design and implementation has been proposed.Independent from any concrete object-oriented method, however, there are threeimportant questions, equally relevant to practitioners and researchers.Firstly, what are the concepts, tasks, and results of analysis, design andimplementation in an object-oriented framework to system development and how dothey relate to each other?Secondly, how does object-oriented system development compare to traditionalapproaches?And thirdly, what are the pitfalls of object-oriented system development andhow to cope with them? The tutorial will provide answers to all three questionsin concert.}
}

@booklet{Engels92,
  title = {Query Languages for the Extended ER Model},
  author = {Gregor Engels},
  howpublished = {Tutorial at the workshop "SION Ph.D. Students Information Systems", Mierlo (The Netherlands)},
  month = {June},
  year = {1992}
}

@booklet{Ebert91,
  title = {Design Description Methods},
  author = {J{\"u}rgen Ebert AND Gregor Engels},
  howpublished = {Tutorial at the European Conference on Software Engineering (ESEC '91), Milano (Italy)},
  month = {October},
  year = {1991}
}