Engineering Modelling Languages: A Precise Meta-Modelling Approach

Abstract

This paper describes a Meta-Modeling Framework (MMF) that addresses many of the deficiencies in the definition of The unified Modeling Language (UML), and promises to support the OMG's newly announced strategy, Model Driven Architecture (MDA) [OMG01]. The facility comprises a language (MML) for defining modeling notations, a tool (MMT) that checks and executes those definitions, and a method (MMM) consisting of a model based approach to language definition and a set of patterns embodying good practice in language definition.The development of MMF by the pUML group ([pUML]) is ongoing and has been supported by IBM and Rational Inc. The work reported in this paper is a simplified version of the work described in out initial submission to the UML 2.0 revision initiative [Cla01] which is expected to be completed in 2002.The need for the definition of UML are recognized, in part, by the infrastructure RFP for UML 2.0 [OMG00]. In Section 3.0 on page 14 we identify some of the main requirements of the RFP, show how these relate to the needs described above, and outline how MMF addresses them. This paper is structured as follows. The three main components (method, language and tool) to the MMF approach is described. The MMF approach is then applied to a simple description of a modelling language. The language, called SML, is a simplified version of a typical object-oriented static modelling language. MMF allows modelling language properties to be defined as a collection of templates. The templates for SML are defined and then used to construct models of syntax and semantics. Finally we place this work into context and outline future work. A Method for Meta-Modelling (MMM)The UML is a collection of notations, some visual some textual. These notations currently have a loose mapping to an abstract syntax (which is imprecisely defined), which in turn is given an informal semantics written in natural language. The UML needs to become a precisely defined family of modeling languages, where a modeling language comprises a notation (concrete syntax), abstract syntax and semantics.Software Engineers define languages as a collection of models with mappings between them. Typically a language consists of models for concrete syntax, abstract syntax and for the semantic domain. Mappings are defined by associating model elements. A language has mappings between concrete syntax and abstract syntax and between abstract syntax and the semantic domain. For example, a language for class diagrams can be defined in terms of a model for boxes and lines, a model for classes, attributes and associations, and a model for objects and slots. A mapping between abstract and concrete syntax relates classes, attributes and associations to boxes, text and lines. A mapping between abstract syntax and the semantic domain relates classes, attributes and associations to objects and slots.The MMF approach applies OO modelling to the definition of OO modelling languages. Each language component is defined as a package containing a class diagram. Package spec...

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“…relation composition), and are nervous about the size of the metamodel that might be required. -Encoding the patterns as package templates [5] [6]. This will provide one approach to taming the complexity of large definitions, not least by allowing whole chunks of metamodel to be generated simply through the substitution of template parameters (templates just provide a formal encoding of the systematic rules we have been using when applying the patterns of section 3).…”

“…These patterns could be captured as package templates, as originally described in the Catalysis method [8], which would effectively systemise and automate the substitution process. Templates have been already been used to encode patterns like this for metamodelling [1] [5]. When applying the pattern, it is usually necessary to add additional constraints stipulating the specific properties of the relation under consideration.…”

“…Metamodelling is perhaps best know in its application to the UML where a subset of UML is used to define (the abstract syntax of) itself [12] -hence the use of 'meta'. Recently, it has been demonstrated that metamodelling can be used to define concrete syntax and semantics, as well as abstract syntax [5] [7][1] [4] [14]. This involves defining a model of concrete syntax and a model of the semantics domain, in addition to a model of abstract syntax, and then modelling, somehow, the transformation relationship between these three components.…”

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“…A model-enhanced version of this diagram would therefore need to be based on a language that is specifically designed to represent cultural forces in an organization -the domain. Such a class of language is often termed a domain specific language (DSL) [6].…”