Invariance, maintenance and other declarative objectives of triggers --
a formal characterization of active databases.
Mutsumi Nakamura and Chitta Baral.
In this paper we take steps towards a systematic design of
active features in an active database. We propose having declarative
specifications that specify the objective of an active database
and formulate the correctness of triggers with respect to such
specifications. In the process 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 correspondence 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.