Conclusions and Future Perspective
The book has described visual programming languages and their applications in several important domains. We started with a general introduction to the concepts of visual languages and presented a theory behind such languages, i.e. a context-sensitive graph grammar formalism, known as the reserved graph grammar (RGG). The RGG was based but improved on the LGG (Rekers and Schürr 1997). By keeping the layer decomposition mechanism of the LGG to terminate parsing in finite steps, the RGG uses a marking technique with an embedding rule to solve the embedding problem. The rule ensures that the application of a production in the graph rewriting process would not create dangling edges. By ensuring selectionfree productions in the RGG, sometimes called confluent graph grammars elsewhere, a selection-free parsing algorithm (SFPA) attempts only one parsing path and thus achieves a polynomial time complexity. It is difficult to estimate how many types of diagrams could be specified by selectionfree productions. Having applied RGGs to many different application domains, we have not come across a diagram formalism that cannot be specified by selection-free productions.
KeywordsGraph Transformation Graph Grammar Visual Language Grammar Formalism Attribute Grammar
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