Handle-rewriting hypergraph grammars

Abstract

We introduce the handle-rewriting hypergraph grammars (HH grammars), based on the replacement of handles, i.e., of subhypergraphs consisting of one hyperedge together with its incident vertices. This extends hyperedge replacement, where only the hyperedge is replaced. A HH grammar is separated (an S-HH grammar) if nonterminal handles do not overlap. The S-HH grammars are context-free, and the sets they generate can be characterized as the least solutions of certain systems of equations. They generate the same sets of graphs as the NLC-like vertex-rewriting C-edNCE graph grammars that are also context-free.