Single vs. Double pushout derivations of graphs

Abstract

Graph grammars in which the generation of graphs using productions and restricting derivation sequences based on the double pushout, recently introduced by H. Ehrig and the author and motivated by modular software design, are shown to have strictly more expressive power than those using derivations based on the single pushout approach of [12]. Furthermore, not being based on the internal structure of graphs, the approach can be immediately generalized to other formalisms, such as algebraic specifications, jungles, etc.