Invariance, maintenance, and other declarative objectives of triggers - A formal characterization of active databases

Abstract

In this paper we take steps towards a systematic design of active features in an active database. We propose having declarative spec- ifications that specify the objective of an active database and formulate the correctness of triggers with respect to such specifications. In the pro- cess we distinguish between the notions of 'invariance' and 'maintenance' and propose four different classes of specification constraints. We also propose three different types of triggers with distinct purposes and show through the analysis of an example from the literature, the correspon- dence between these trigger types and the specification classes. Finally, we briefly introduce the notion of k-maintenance that is important from the perspective of a reactive (active database) system.