Stuart Kent

Model Driven Engineering

The Object Management Groups (OMG) Model Driven Architecture (MDA) strategy envisages a world where models play a more direct role in software production, being amenable to manipulation and transformation by machine. Model Driven Engineering (MDE) is wider in scope than MDA. MDE combines process and analysis with architecture. This article sets out a framework for model driven engineering, which can be used as a point of reference for activity in this area. It proposes an organisation of the modelling space and how to locate models in that space. It discusses different kinds of mappings between models. It explains why process and architecture are tightly connected. It discusses the importance and nature of tools. It identifies the need for defining families of languages and transformations, and for developing techniques for generating/configuring tools from such definitions. It concludes with a call to align metamodelling with formal language engineering techniques.

Spider Diagrams

Spider diagrams combine and extend Venn diagrams and Euler circles to express constraints on sets and their relationships with other sets. These diagrams can be used in conjunction with object-oriented modelling notations such as the Unified Modelling Language. This paper summarises the main syntax and semantics of spider diagrams. It also introduces inference rules for reasoning with spider diagrams and a rule for combining spider diagrams. This system is shown to be sound but not complete. Disjunctive diagrams are considered as one way of enriching the system to allow combination of diagrams so that no semantic information is lost. The relationship of this system of spider diagrams to other similar systems, which are known to be sound and complete, is explored briefly.

Constraint diagrams: visualizing invariants in object-oriented models

A new visual notation is proposed for precisely expressing constraints on object-oriented models, as an alternative to mathematical logic notation used in methods such as Syntropy and Catalysis. The notation is potentially intuitive, expressive, integrates well with existing visual notations, and has a clear and unambiguous semantics. It is reminiscent of informal diagrams used by mathematicians for illustrating relations, and borrows much from Venn diagrams. It may be viewed as a generalization of instance diagrams.

Precise Visual Specification of Design Patterns

There has been substantial recent interest in captured design expertise expressed as design patterns. Prevalent descriptions of these design patterns suffer from two demerits. Firstly, they capture specific instances of pattern deployment, rather than the essential pattern itself, thus the spirit of the pattern is often lost in the superfluous details of the specific instances described. Secondly, existing pattern descriptions rely upon relatively informal diagrammatic notations supplemented with natural language annotations. This can result in imprecision and ambiguity. This paper addresses these problems by separating the specification of patterns into three models (role, type, and class). The most abstract (role-centric) model presents patterns in their purest form, capturing their essential spirit without deleterious detail. A role-model is refined by a type-model (adding usually-domain-specific constraints), which is further refined by a class-model (forming a concrete deployment). We utilise recent advances in visual modelling notation to achieve greater precision without resorting to obtuse mathematical symbols. A set-oriented view of state, operations, and instances is adopted, permitting their abstract presentation in models via this visual notation. This paper utilises these ideas in the unambiguous specification of a selection of prominent design patterns. The expectation is that precise visual pattern specification will firstly enable clear communication between domain experts and pattern writers (and ultimately pattern users), and secondly enable CASE tool support for design patterns, permitting the designer (pattern user) to operate at a higher level of abstraction without ambiguity.

A Relational Approach to Defining Transformations in a Metamodel

Metamodelling is becoming a standard way of defining languages such as the UML. A language definition distinguishes between concrete syntax, abstract syntax and semantics domain. It is possible to define all three using a metamodelling approach, but it is less clear how to define the transformations between them. This paper proposes an approach which uses metamodelling patterns that capture the essence of mathematical relations. It shows how these patterns can be used to define both the relationship between concrete syntax and abstract syntax, and between abstract syntax and semantics domain, for a fragment of UML. A goal of the approach is to provide a complete specification of a language from which intelligent tools can be generated. The extent to which the approach meets this goal is discussed in the paper.

Core meta-modelling semantics of UML: the pUML approach

The current UML semantics documentation has made a significant step towards providing a precise description of the UML. However, at present the semantic model it proposes only provides a description of the languages syntax and well-formedness rules. The meaning of the language, which is mainly described in English, is too informal and unstructured to provide a foundation for developing formal analysis and development techniques. Another problem is the scope of the model, which is both complex and large. This paper describes work currently being undertaken by the precise UML group (pUML), an international group of researchers and practitioners, to address these problems. A formalisation strategy is presented which concentrates on giving a precise denotational semantics to core elements of UML. This is illustrated through the development of precise definitions of two important concepts: generalization and packages. Finally, a viewpoint architecture is proposed as a means of providing improved separation of concerns in the semantics definition.

The Metamodelling Language Calculus: Foundation Semantics for UML

The Metamodelling Language (MML) is a sub-set of the Unified Modeling Language (UML) that is proposed as the core language used to bootstrap the UML 2.0 definition initiative. Since it is meta-circular, MML requires an external formal semantics in order to ground it. This paper defines the MML Calculus which is used to formally define MML and therefore provides a semantic basis for UML 2.0.

A relational approach to defining and implementing transformations between metamodels

The Model-Driven Architecture initiative of the OMG promotes the idea of transformations in the context of mapping from platform independent to platform specific models. Additionally, the popularity of XML and the wide spread use of XSLT has raised the profile of model transformation as an important technique for computing. In fact, computing may well be moving to a new paradigm in which models are considered first class entities and transformations between them are a major function performed on those models. This paper proposes an approach to defining and implementing model transformations which uses metamodelling patterns to capture the essence of mathematical relations. It shows how these patterns can be used to define the relationship between two different metamodels. A goal of the approach is to enable complete specifications from which tools can be generated. The paper describes implementations of the examples, which have been partially generated from the definitions using a tool generation tool. A number of issues emerge which need to be solved in order to achieve the stated goal; these are discussed.

Engineering Modelling Languages: A Precise Meta-Modelling Approach

MMF uses meta-modelling techniques to precisely define modelling languages. The approach employs novel technology based on package specialisation and templates. MMF is being applied to the UML 2.0 revision initiative and is supported by a tool.

Formalizing spider diagrams

Geared to complement UML and the specification of large software systems by non-mathematicians, spider diagrams are a visual language that generalizes the popular and intuitive Venn diagrams and Euler circles. The language design emphasizes scalability and expressiveness while retaining intuitiveness. In this paper, we describe spider diagrams from a mathematical standpoint and show how their formal semantics can be made in terms of logical expressions. We also claim that all spider diagrams are self-consistent.