Publisher-subscriber: An agent system for notification of versions in OODBs

In object-oriented databases, the conceptual structure may not be constant and may vary due to variety of reasons like correcting mistakes, adding/removing features, updating database, etc. Class versioning is one the evolution strategy that addresses the above issues. However, class versioning may be yields some unexpected results to the database clients. The easiest method is to just set a cache to expire periodically depending on the types of data. This solution is approximation and tends to either refresh too often so that the data is unnecessarily sent over the network or not often enough so that the data becomes stale. Query notification is the solution to avoid frequent access to the database and hence proposed to design agent system for monitoring class versioning. agent technology has generated lots of excitement in recent years because of its promise as a new paradigm for conceptualizing, designing and implementing software systems. Software agents coordinate the application that run on databases and allows performing the sequence of events like flushing cache, database operations, monitoring, etc. This agent system consists of a publisher agent, subscriber agents and a database update agent. These agents monitor the database for any change that would change data the data in the query or its structure. When it detects such a change, the publisher agent generates a change notification message and subscriber agent subscribes the notification message. To implement this system, a database application was developed with two versions and applied the database change notifications. To promote more reusability and scalability, a publisher-subscriber pattern was integrated with this application.