An NCE context-sensitive graph grammar for visual design languages

An NCE context-sensitive graph grammar, that is, a context-sensitive graph grammar with neighborhood controlled embedding has been developed. It is an expansion of the well-known NCE (context-free) graph grammar. Because it has a quite general embedding mechanism, it can be used to formalize the graph-syntax rules of visual objects with much flexibility. The composition of its production copies is discussed. It is theoretically and practically significant for defining graph-rewriting rules that can be (re)used to embed sub-graphs of particular structures, such as the feedback structure of control systems and the frequently-used sub-diagrams of program diagrams. The confluence property of NCE context-sensitive graph grammars is also studied. This property maintains that the result of a derivation does not depend on the order in which the production copies were applied. This is very important for guaranteeing the validity of the application of composite production copies and for developing efficient parsing algorithms. This formalization of subgraph reuse on, the basis of composite production copies is widely applicable to visual design languages based on graph grammars.