Visual Patterns Associated to Abstract Trees

AbstractVisual languages have an important role in modeling systems, specification of software, and in specific application domains. By using visual properties like spatial placement or line connections complex structures can be presented, so that humans can understand them quickly. Visual languages can be based on domain-specific metaphors, so that domain specialists can use their conventional way of description and abstraction.For working with a visual language, a specialized graphical frontend is needed. In contrast to textual languages, general purpose editors are insufficient for visual languages, because each visual language has its particular graphical requirements. The frontend should provide methods to aid efficient drawing and restructuring of visual expressions. Often, language-specific structure editors are used as frontends for visual languages. The visual program is stored in a language-dependent data structure. The user interacts with one or more visual representations. Edit operations are directly applied to the underlying structure and after a change the graphical representation is recomputed.The implementation of visual languages requires a wide range of conceptual and technical knowledge from issues of user interface design and graphical implementation to aspects of analysis and transformation for languages in general. We present a powerful toolset that incorporates such knowledge [C. Schmidt and U. Kastens. Implementation of visual languages using pattern-based specifications. Software - Practice and Experience, 35(2):121–131, Nov. 2003]. It generates editors from high level specifications: A language is specified by identifying certain patterns in the language structure, selecting a visual representation from a set of precoined solutions, and associating the pattern to constructs of the abstract grammar. A complete visual structure editor is generated from such a specification. It represents visual programs by attributed abstract trees. Therefore, further phases of processing visual programs can be generated by state-of-the-art tools for compiler construction. Even challenging visual languages can be implemented with reasonable small effort and with rather limited technical knowledge. The approach is suitable for a large variety of visual language styles