An Execution Model for Active Data Base Management Systems

Abstract This paper introduces an execution model for active DBMS's. An active DBMS, besides processing explicit requests from users, automatically performs predefined actions triggered by the occurrence of particular events. Triggered actions are specified by rules that consist of an event, a condition, and an action. When the event occurs, the condition is evaluated and, if true, the action is executed. Our model of execution allows decoupling of the triggering event, condition evaluation, and the triggered action. Coupling modes are defined for rules that determine when, relative to the triggering event and transaction boundaries, the condition is evaluated and the action is executed. A model based on nested transactions is developed to model the behavior of the combined execution of user requests and triggered rules. Concurrency control algorithms are given to implement this model. This work was supported by the Defense Advanced Research Projects Agency and by the Rome Air Development Center under Contract No. F30602-87-C-0029. The views and conclusions contained in this report are those of the authors and do not necessarily represent the official policies of the Defense Advanced Research Projects Agency, the Rome Air Development Center, or the U.S. Government.