Semantic Update Optimization in Active Databases

Abstract

In an active database, an update may be constrained by integrity constraints, and may also trigger rules that, in turn, may affect the database state. The general problem is to effect the update while also managing the “side-effects” of constraint enforcement and rule execution. In this paper an update calculus is proposed by which updates, constraints and rules are specified and managed within the same formalism. Constraints and production rules are expressed in a constraint language based on first-order logic. These logic expressions are used to semantically transform an original update into a sequence of updates that reflect the relevant constraints and production rules. The inference mechanism associated with processing a reformulated query ensures that: 1) the pre- and post-conditions of an update are satisfied, 2) update side-effects are propagated, and 3) repairs are made to tuples exhibiting constraint violations. Thus, a user-specified “update” is transformed, through semantic reformulation techniques, into a sequence of updates which together ensure semantic integrity of the original update as well as its propagated side-effects.This research presents several contributions. Integrity constraints and production rules are expressed in a declarative formalism so that they may be reasoned about. The update calculus formalism handles the semantic reformulation of an update to reflect relevant constraints and rules governing it. Finally, an algorithm is presented to handle constraint enforcement, production rule firing, and subsequent repair actions.