Active Object Systems

Abstract

Active database systems have been proposed to satisfy the requirements of applications that must react in a timely manner to events. Active object systems combine the properties of active database management systems and object-oriented database management systems (OODBMS). This chapter introduces a working model for active objects that attempts to unify the notions of active objects common in databases, operating systems and programming languages. It reviews their basic properties and presents an overview of current developments in active object systems. The structure of event-condition-action rules is presented. Event hierarchies and algebras, condition evaluation and action execution are discussed. The two basic components of the execution model of an active object system are presented: the coupling modes between triggering transaction and triggered rule, and transaction models. Architectural issues are briefly reviewed and correctness criteria and tools for rule definition and execution are discussed.