AN INNOVATIVE APPROACH FOR OBJECT RETRIEVAL IN OBJECT-ORIENTED DATABASES: DIRECT ACCESS METHOD.

Abstract

Query processing remains one of the important challenges of Object-Oriented Database Management Systems. Cost based query optimization involves creating alternative executing plans for a given query and executing the least costly one within a cost model framework. In Object-Oriented Database Management Systems (OODBMSs) objects may store references to other objects (precomputed joins), and path expressions are used in query languages. Although the cost formulas for explicit joins and the selectivity’s of attributes and joins are well-known in the relational model, there is no similar work involving path expressions for OODBMSs. However in order to optimize object-oriented queries involving path expressions, a cost model is essential. This information is necessary for deciding whether to use pointer chasing or to convert the path expressions into explicit joins and also for deciding the execution order of path expressions. In this paper, we propose a query optimization technique that fully utilize the advantages of class Ids and object Ids in object oriented database systems. We present a new access method, called the Direct Access Method, for supporting contained objects in object-oriented databases. We have taken the advantage of generation of class and object Ids which follows particular pattern while creating the classes and objects. The result shows that this method is significantly better than the existing path index method over a wide range of parameters in terms of retrieval of data. An implementation based on the C#.NET system demonstrates the validity of the results.