Key constraints and monotonic aggregates in deductive databases

Abstract

We extend the fixpoint and model-theoretic semantics of logic programs to include unique key constraints in derived relations. This extension increases the expressive power of Datalog programs, while preserving their declarative semantics and efficient implementation. The greater expressive power yields a simple characterization for the notion of set aggregates, including the identification of aggregates that are monotonic with respect to set containment and can thus be used in recursive logic programs. These new constructs are critical in many applications, and produce simple logic-based formulations for complex algorithms that were previously believed to be beyond the realm of declarative logic. © Springer-Verlag Berlin Heidelberg 2002.