Metamodel specialization for graphical language support

Abstract

Most of current modeling languages are based on graphical diagrams. The concrete graphical syntax of these languages typically is defined informally—by text and diagram examples. Only recently, starting from UML 2.5, a formalism is offered for defining the graphical syntax of UML. This formalism is based on Diagram Definition standard by OMG, where the main emphasis is on enabling diagram interchange between different tools implementing the given language. While this is crucial for standardized languages such as UML, this aspect is not so important for domain-specific languages. In this paper, an approach is offered for a simple direct definition of concrete graphical syntax by means of metamodels. Metamodels are typically used for a language definition, but mainly the MOF-inspired approach via meta-metamodel instantiation is used. We offer an alternative approach based on core metamodel specialization which leads to a more direct and understandable definition staying at the same meta-layer. In addition, our approach permits a natural extension—facility for a graphical editor definition for the given language, which is vital in the world of DSLs. In contrast to most DSL development platforms, which are based on the abstract syntax metamodel of the language and a mapping to graphics, our facility is based directly on the graphical syntax. But we show that in those cases where the relation to the DSL abstract syntax is really required, a mapping from the graphical syntax to abstract syntax can be relatively easily defined by the specialization approach.