Theory and Practice of Logic Programming

Properties of Input-Consuming Derivations

a1 Dipartimento di Informatica, Università di Venezia, via Torino 155, 30172 Venezia, Italy (e-mail:,
a2 Department of Computer Science, University of Maastricht, P.O. Box 616, 6200 MD Maastricht, The Netherlands (e-mail:
a3 CWI – Center for Mathematics and Computer Science, P.O. Box 94079, 1090 GB Amsterdam, The Netherlands


We study the properties of input-consuming derivations of moded logic programs. Input-consuming derivations can be used to model the behavior of logic programs using dynamic scheduling and employing constructs such as delay declarations. We consider the class of nicely-moded programs and queries. We show that for these programs a weak version of the well-known switching lemma holds also for input-consuming derivations. Furthermore, we show that, under suitable conditions, there exists an algebraic characterization of termination of input-consuming derivations.

Key Words: dynamic scheduling; termination.