Query Optimization Techniques Utilizing Path Indexes in Object-Oriented Database Systems

We propose query optimization techniques that fully utilize the advantages of path indexes in object-oriented database systems. Although path indexes provide an eecient access to complex objects, little research has been done on query optimization that fully utilize path indexes. We rst devise a generalized index intersection technique, adapted to the structure of the path index extended from conventional indexes, for utilizing multiple (path) indexes to access each class in a query. We then propose the query graph reduction algorithm that replaces the classes in the query graph with path index scans; we call the resultant query graph reduced query graph (RQG). We nally present the search algorithm that nds the least-cost evaluation plan from RQG based on a cost model. Proposed query optimization techniques enhance database performance by using path indexes instead of direct accesses to data in the evaluating queries.