Filters for Graph Matching

. This paper shows how structure may be used as necessary conditions or filters for matching in graphical knowledge representations i.e. detecting, without doing a full graph comparison, that one graph cannot match or subsume another. In injective subsumption domains each node of a subsumed graph is matched by only one node of a subsuming graph so all graphs are irreducible and there are several possible filters, e.g. node degrees and cycle lengths. For example in chemical formulae, in which subsumption is `part-of', a formula containing a cycle cannot subsume another formula that does not contain a cycle of the same length. Few such filters exists for more general subsumption, in which a node of a subsumed graph may be matched by several nodes of a subsuming graph, but many graphs contain subgraphs that are irreducible because the node labels are not unifiable. Injective subsumption filters may be applied to irreducible subgraphs but computing irreducible subgraphs is in general intra..