Design of Sentinel: an object-oriented DMBS with event-based rules

Abstract

This paper describes the design of event-condition-action (ECA) rules for supporting active capability in an object-oriented DBMS and sketches its incorporation in a C++ environment. We summarize Snoop—an expressive event specification language which supports temporal, explicit, and composite events in addition to the traditional database events. A small set of event operators is introduced for building composite events. We also introduce an event interface to extend the conventional object semantics to include the specification of primitive events. This interface is used as a basis for the specification of events spanning objects, possibly from different classes, and detection of primitive and composite events. New rules can be introduced on existing objects, enabling objects to react to their own changes as well as to the changes of other objects. We introduce a runtime subscription mechanism between rules and objects to monitor objects selectively. This mechanism elegantly supports class level as well as instance level rules. Finally, using an illustrative example, we compare the functionality of our approach with related work.