Defining and Parsing Visual Languages with Layered Graph Grammars

Sentences of Visual Languages (VLs) may often be regarded as assemblies of pictorial objects with spatial relationships like “above” or “contains” between them, i.e. their representations are a kind of directed graphs. Such a spatial relationship graph is often complemented by a more abstract graph, which provides information about the syntax (and the semantics) of the visual sentence in a more succinct form. As both representations are graphs, graph grammars are a natural means for defining the concrete and the abstract syntax of VLs. They can be used to generate syntax directed VL editors, which support “free editing” and parsing of their underlying graph structures. Unfortunately, all efficiently working graph grammar parsing algorithms deal with restricted classes of context-free graph grammars only, while more general classes of graph grammars are necessary for defining many VLs. This motivated us to develop the notion of layered context-sensitive graph grammars, together with a bottom-up/top-down parsing algorithm.