Rules are objects too: A knowledge model for an active, object-oriented database system

Abstract

Event-Condition-Action (ECA) Rules are proposed as a general mechanism for providing active database capabilities in support of applications that require timely response to critical situations. These rules generalize mechanisms such as assertions, triggers, alerters, database procedures, and production rules that have previously been proposed for supporting such DBMS functions as integrity control, access control, derived data management. and inferencing. This paper argues that ECA rules should be thought of as first class objects in an object-oriented data model. It identifies concepts for modelling the components and properties of rule objects: events (database operations, temporal events, abstract signals from arbitrary user processes, and complex events constructed from these primitive ones); conditions (queries over the database): actions (programs in the query language or some programming language); and coupling modes (which describe whether the event, condition, and action components of a rule should be executed in a single transaction or in separate transactions). The paper discusses the association of timing constraints and contingency plans with rules. Finally, it describes operations on rule objects. The emphasis of the paper is on modelling concepts, rather than on specific syntax.