A Language Definition Method for Visual Specification Languages

Language definition is always an important topic in the field of computer science. For textual specification and programming languages, there are already lots of mature methods of language definition. However, for visual specification languages, especially the so called wide spectrum graphical modelling languages, the existing solutions are far from satisfactory. ADORA[27] is a modelling technique for requirements and software architecture that is being developed in the Requirement Engineering Research Group, University of Zurich. The acronym stands for Analysis and Description of Requirements and Architecture. ADORA and UML are typical examples of wide spectrum graphical modelling languages. In this dissertation, we propose a new method of defining visual specification languages, which shall overcome the drawbacks of the existing definition methods. The ADORA Language, which is used to model system requirements and software architecture, is selected as a vehicle for demonstrating our method. The following four aspects of language definition are particularly addressed: • Syntax and static semantics definition A text-based technique is given for the syntax and static semantics definition. We exploit the fact that in a visual specification language, most syntactic features are independent of the layout of the graph. So we map the graphical elements to textual ones and define the context-free syntax of this textual language in EBNF. Using our mapping, this grammar also defines the syntax of the graphical language. Simple spatial and contextsensitive constraints are then added by attributing the context-free grammar. Finally, for handling complex structural and dynamic information in the syntax, most of which is also called static semantics in the literature, we give a set of operational rules that work on the attributed EBNF. We also extend this set of operational rules to specify an advanced feature of ADORA, which supports the description of partial and evolutionary specifications. • Dynamic semantics definition We propose a strategy of dynamic semantics definition for ADORA: instead of defining a formal semantics for the whole language at one time, which can be too complex to be