On Termination of Graph Rewriting

A necessary and sufficient condition for termination of graph rewriting systems is established. Termination is equivalent to the finiteness of all forward closures, being certain minimal derivations in which each step depends on previous steps. This characterization differs from corresponding results for term rewriting in that the latter hold only for subclasses of term rewriting systems. When applied to term graph rewriting, the result characterizes termination of arbitrary term rewriting systems under graph rewriting. In particular, it captures non-terminating term rewriting systems that are terminating under graph rewriting.