Subsumption for Semantic Query Optimization in OODB

The purpose of semantic query optimization is to use semantic knowledge (e.g. integrity constraints) for transforming a query into an equivalent one that may be answered more efficiently than the original version. This paper proposes a general method for semantic query optimization in the framework of OODBs (Object Oriented Database Systems). The method is applicable to the class of conjunctive queries and is based on two ingredients: a description logic able to express both class descriptions and integrity constraints rules (IC rules) as types; subsumption computation between types to evaluate the logical implications expressed by IC rules. 1 Introduction In database environment, semantic knowledge is usually expressed in terms of IC rules, that is if then rules on the attributes of a database schema (i.e., roughly a Tbox of a Terminological Knowledge Representation System (TKRS)). Informally, semantic equivalence means that the transformed query has the same answer as the origina..