A Petri Net Based Simulator For Active Database Systems

Abstract

Active database systems were introduced to extend the database functionality. As well as a repository of data, active database can detect the occurrence of events in a database system and react automatically to that event occurrence and execute certain actions either inside or outside the database. This behavior is specified by means of ECA (event-condition-action) rules, i.e., when an event has occurred, if the condition is evaluated to true, then an action is executed. The development of a set of ECA rules involve the knowledge of the database structure and the relationships that can exist among the ECA rules, which may produce an inconsistent state in the database. Therefore, it is so important to verify a rule set before its implementation in the active database, and one method to determine if a rule set will produce consistent states of the database is through the simulation of ECA rule firing. In this paper a simulator for active databases, named ECAPNSim, is described. ECAPNSim uses the definition of ECA rules like a structure of an extended Petri net model, the Conditional Colored Petri Net (CCPN). Conditional Colored Petri Net definition involves the knowledge and execution model, which describe the features that an active database system must have. Furthermore, in order to simulate the occurrence of database events, ECAPNSim has been enhanced with the addition of distribution functions for each place that denote events of the ECA rule set.