Design of a New Indexing Organization for a Class-Aggregation Hierarchy in Object-Oriented Databases

In an object oriented databases a class consists of a set of attributes and the values of the attributes are objects that belong to other classes that is the de nition of a class forms a class aggregation hierarchy of classes A branch of such a hierarchy is called a path There have been several index organizations proposed to support object oriented query languages including multiindex join index nested index and path index In all the proposed index organizations they are helpful only to a query which retrieves the objects of the root class of a given path by a predicate which speci es the value of the attribute at the end of the path In this paper we propose a new index organization for evaluating queries called full index where an index is allocated for each class and its attribute or nested attribute along the path From the analysis results we show that a full index can support any type of queries along a given path with a lower retrieval cost than all the other index organizations Moreover to reduce the high update cost for a long given path we will split the path into several subpaths and to allocate a separate index on each subpath Given a path the number of subpaths and the index organization of each subpath de ne an index con guration Since a low retrieval cost and a low update cost are always a trade o in all index organizations we also propose cost formulas to determine the index con guration which can provide the best performance for various applications by taking into account various types of queries along a given path and a set of queries with more than one nested predicates along a given path