Integrity maintenance systems: an architecture

Abstract

In conventional database systems, consistency is preserved either by forbidding operations that violate integrity constraints or by rolling back transactions that produce inconsistent database states. A third way to maintain integrity is that of post-processing faulty transactions, by introducing system-generated compensating actions that lead to a database state that is consistent andas close as possible to that intended by the user. Active databases, which couple production rules to database processing, provide the appropriate technology to implement compensating actions. In this paper, we presentan architecture for integrity constraint maintenance systems, which provides severa! facilities to support the different phases of the process of constraint maintenance, going from compile-time tasks, like constraints specification, rule generation and rule analysis, to the run-time control of transactions in presence of constraint enforcing rules. Particular emphasis is placed on the task of analyzing a set of automatically generated compensating actions, to ensure correctness, termination and semantic adequacy of the constraint maintenance system. We provide a hypergraph-based representation of this problem, investigate its complexity and propase a heuristic solution.