Reiko Heckel

GRAPH GRAMMARS WITH NEGATIVE APPLICATION CONDITIONS

In each graph-grammar approach it is defined how and under which conditions graph productions can be applied to a given graph in order to obtain a derived graph. The conditions under which productions can be applied are called application conditions. Although the generative power of most of the known general graph-grammar approaches is sufficient to generate any recursively enumerable set of graphs, it is often convenient to have specific application conditions for each production. Such application conditions, on the one hand, include context conditions like the existence or non-existence of nodes, edges, or certain subgraphs in the given graph as well as embedding restrictions concerning the morphisms from the left-hand side of the production to the given graph. In this paper, the concept of application conditions introduced by Ehrig and Habel is restricted to contextual conditions, especially negative ones. In addition to the general concept, we state local confluence and the Parallelism Theorem for derivations with application conditions. Finally we study context-free graph grammars with application conditions with respect to their generative power.

Confluence of Typed Attributed Graph Transformation Systems

The issue of confluence is of major importance for the successful application of attributed graph transformation, such as automated translation of UML models into semantic domains. Whereas termination is undecidable in general and must be established by carefully designing the rules, local confluence can be shown for term rewriting and graph rewriting using the concept of critical pairs. In this paper, we discuss typed attributed graph transformation using a new simplified notion of attribution. For this kind of attributed graph transformation systems we establish a definition of critical pairs and prove a critical pair lemma, stating that local confluence follows from confluence of all critical pairs.

Tutorial Introduction to Graph Transformation: A Software Engineering Perspective

We give an introduction to graph transformation, not only for researchers in software engineering, but based on applications of graph transformation in this domain. In particular, we demonstrate the use of graph transformation to model object- and component-based systems and to specify syntax and semantics of diagram languages. Along the way we introduce the basic concepts, discuss different approaches, and mention relevant theory and tools.

Dynamic meta modeling: a graphical approach to the operational semantics of behavioral diagrams in UML

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 specification of the systems dynamics by means of collaboration diagrams. In this way, it is possible to define the behavior of UML diagrams within UML. The conceptual idea is inherited from Plotkins structured operational semantics (SOS) paradigm, a style of semantics specification 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 state-chart 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.

A methodology for specifying and analyzing consistency of object-oriented behavioral models

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, we 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.

Ensuring Consistency of Conditional Graph Grammars - A Constructive Approach -

Abstract Consistency conditions describe basic properties of graphs as e.g. the existence or uniqueness of certain elements. A graph grammar is consistent if the start graph satisfies the consistency condition and the rules preserve this property. We propose a general construction that transforms global consistency conditions into preconditions for individual rules. A so-constructed rule is applicable to a consistent graph if and only if the derived graph is consistent, too. The relevance of this result is motivated by an example specification of a safety-critical system that is, a roundabout.

Graph Transformation in a Nutshell

Even sophisticated techniques start out from simple ideas. Later, in reply to application needs or theoretical problems new concepts are introduced and new formalisations proposed, often to a point where the original simple core is hardly recognizably. In this paper we provide a non-technical introduction to the basic concepts of typed graph transformation systems, completed by a survey of more advanced concepts, and explain some of its history and motivations.

Towards Contract-based Testing of Web Services

Web Services are composed by linking together service providers and requestors. To ensure interoperability, the requestors requirements for a service have to be matched against a service description offered by the provider.Besides data types and operation signatures, this requires service specifications to include behavioral information, like contracts specifying pre- and post-conditions of (required or provided) operations.In this paper, we propose to visualize contracts by graph transformation rules which blend well with a UML-based notion of data models and signatures. The operational interpretation of rules could turn out to be useful for simulating the behavior of required components in unit testing.

Automatic conformance testing of web services

Web Services are the basic building blocks of next generation Internet applications, based on dynamic service discovery and composition. Dedicated discovery services will store both syntactic and behavioral descriptions of available services and guarantee their compatibility with the requirements expressed by clients. In practice, however, interactions may still fail because the Web Services implementation may be faulty. In fact, the client has no guarantee on the quality of the implementation associated to any service description. In this paper, we propose the idea of high-quality service discovery incorporating automatic testing for validating Web Services before allowing their registration. First, the discovery service automatically generates conformance test cases from the provided service description, then runs the test cases on the target Web Service, and only if the test is successfully passed, the service is registered. In this way, clients bind with Web Services providing a compatible signature, a suitable behavior, and a high-quality implementation.

Rule-Based Specification of Behavioral Consistency Based on the UML Meta-model

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 different consistency notions. Therefore, general meta-level techniques are required for specifying, analyzing, and communicating consistency constraints. In this paper, we discuss the issue 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.