A generalization of finite-state automata that is used to represent natural-language grammars and hence to parse and generate natural-language text (see parsing, natural-language understanding). The grammar is represented as a set of labelled directed graphs whose labels are word categories, or recursive calls to itself or other graphs, or calls to update or access a set of registers. Procedures can be associated with the arcs to build a parse tree or a semantic representation, or to generate text, etc.