The HiPAC project is investigating active, time-constrained database managment. An active DBMS is one which automatically executes specified actions when speciifed conditions arise. HiPAC has proposed Event-ConditionAction (ECA) rules as a formalism for active database capabilities. We have also developed an execution model that speicifes how these rules are processed in the context of database transactions. The additional functionality provided by ECA rules makes new demands on the design of an active DBMS. In this paper we propose an architecture for an active DBMS that supports ECA rules. This architecture provides new forms of interaction, in support of ECA rules, between application programs and thDBMS.This leads to a new paradigm for constructing database applications.

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The HiPAC (High Performance ACtive database system) project addresses two critical problems in time-constrained data management: the handling of timing constraints in databases, and the avoidance of wasteful polling through the use of situation-action rules that are an integral part of the database and are monitored by DBMS's condition monitor. A rich knowledge model provides the necessary primitives for definition of timing constraints, situation-action rules, and precipitating events. The execution model allows various coupling modes between transactions, situation evaluations and actions, and provides the framework for correct concurrent execution of transactions and triggered actions. Different approaches to scheduling of time-constrained tasks and transactions are explored and an architecture is being designed with special emphasis on the interaction of the time-constrained, active DBMS and the operating system. Performance models are developed to evaluate the various design alternatives.

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