Invariance , Maintenance and other declarativeobjectives of triggers { a formal characterizationof active databasesMutsumi

In this paper we take steps towards a systematic design of active features in an active database. We propose having declarative speciications that specify the objective of an active database and formulate the cor-rectness of triggers with respect to such speciications. In the process we distinguish between the notions ofìnvariance' and`maintenance' and propose four diierent classes of speciication constraints. We also propose three diierent types of triggers with distinct purposes and show through the analysis of an example from the literature, the correspondence between these trigger types and the speciication classes. Finally, we brieey introduce the notion of k-maintenance that is important from the perspective of a reactive (active database) system.