Active object-oriented database systems for CIM applications

Abstract

Object-oriented database systems (OODBS) have gained wide attention as the most promising database technology for non-standard applications like computer aided design and computer integrated manufacturing. Among the most important requirements of these applications which are supported by OODBS are complex object modeling, advanced transaction management, and version management, to mention just a few. Active database systems (ADBS) have reached equal potential for non-standard applications as they offer event driven and constraint driven behavior of the database system necessary for implementing time critical reactions. For example, manufacturing plants need timely support of raw material and assemblies to keep going the manufacturing process. Active object-oriented database systems (AOODBS) provide the best of both worlds. They are based on one hand on an object-oriented data model for representing the objects of the problem domain, and on the other hand on a rule based knowledge model for representing the event driven and constraint driven behavior. In the first part of this chapter we survey various approaches to AOODBS. In the second part we report on our own experience in extending the commercially available OODBS GemStone™ with active capabilities. TriGS (= Trigger system for GemStone) focuses on several concepts that originate both from shortcomings of existing active object-oriented database systems and from advanced requirements of Leitstand systems, for which TriGS has been developed in the first place. TriGS makes explicit use of objects, message passing, inheritance, and overriding to provide for a seamless integration between rules and an object-oriented data model. Rules consisting of events, conditions, and actions monitor the behavior of objects and can be attached to specific classes (local rules) or defined independently of any class hierarchy (global rules). Concerning the execution of rules, TriGS uses a flexible event based mechanism defining the points in time when conditions are evaluated and actions are executed. An evaluation of TriGS and a discussion of future research issues concludes this chapter.