Class reference reduction in object-oriented databases

The authors propose a semantic query-optimizer (SQO) using semantic integrity constraints (SICs) in an object-oriented database system (OODB). SICs assert permissible or consistent database states (a database state is the stored data at a given time instance) for a database application. For example, in a payroll database, the minimum hourly rate has to be $4.35 by law. The basic idea of SQO is to optimize queries by transforming a query qualification into another semantically equivalent one using semantic integrity constraints such that evaluating the transformed query would be less costly. Although semantic query optimization has been well studied in the context of relational and deductive database systems, certain distinct object-oriented features such as IS-A class hierarchy have not been taken into consideration. This is probably due to that OODB is relatively new and that there is lack of research so far on SICs in OODBs