Comparison of two graph-rewrite systems (Q1111401)

In 1972, Ehrig, Pfender and the reviewer proposed a graph-rewriting system, based on a double pushout construction. The paper compares this well known approach to Raoult's version, using only a single pushout of partial morphisms. The paper characterizes the generative power of a graph-rewriting system by a partial function from a class of triples (rewrite rule, graph, redex) into a class of resulting graphs. The main idea is to study pairs of input triples that are analogous in some sense. The main result is as follows: Analogous productions that additionally satisfy Ehrig's gluing condition, are equivalent. This result was already given by Raoult, but the author uses a weaker, still sufficient condition. The paper is difficult to read; the interested reader should be familiar with the referenced literature.