Conditional transactions: A model of computation for active databases

This paper introduces a transaction model for active databases. Concurrent execution of rules needs to be carefully managed to ensure consistent semantics. It is shown that serializability is not always sufficient for correctness. A new criterion, conditional conflict serializability (CCS) is developed and shown to ensure the desired correctness. A graph based scheduler for it is presented. Practical schedulers should also be recoverable, which the graph based scheduler is not. We next prove that conventional 2-phase locking also achieves CCS, and can thus be used in practice.