On Termination of Datalog Programs*: Extended Abstract

Datalog programs (i.e., function-free logic programs) are considered. It is assumed that EDB predicates satisfy some monotonicity constraints, and the paper addresses the problem of whether a given program and query yield (for some EDB relations) a top-down evaluation tree with an infinite path. The lack of an infinite path essentially means that a Prolog interpreter can find all answers in finite time. A necessary and sufficient condition for the lack of an infinite path is given assuming that EDB relations are finite. A sufficient condition is given assuming that EDB relations could be infinite.