The hcC-tree: An Efficient Index Structure for Object Oriented Databases

Object oriented database systems, in contrast to traditional relational database systems, allow the scope of a query against a class to be either the class itself or all classes in the class hierarchy rooted at the class. If object oriented databases have to achieve acceptable performance levels against such queries, we need indexes that support efficient retrieval of instances from a single class as well as from all classes in a class hierarchy. In this pa per, we propose a new index structure called h&-tree (hierarchy class Chain tree) that sup ports both kinds of retrieval &ciently. Moreover, the update cost of the index structure is bounded by the h$ght of the h&-tree. We have implemented hcC-trees along with Htrees and CH-trees (two other index structures that have been proposed in the literature) and report a detailed performance analysis of the three structures. The performance study reveals that h&-trees perform much better than the other two structures under most circumstances. The balanced behaviour of hcC-tree under all kinds of queries and in the presence of updates shows that it is a promising index structure for the future. Pcmbiarion to copy without fee all or pori of thb material ti gnanted provided that the copier are not made or di&ibuted jor direct commercial adrantapc, the VLDB copMht notice and the title of the publication and itr date appear, and notice ia piwen that cop&l in bp permiwion of the V&p La-c Data Bare Bndowment. To copy othcrwiw, or to -b&h, rcqminr a jee and/or special permkkn jwm the Endowment. Proceed&p of the 20th VLDB Conference Santiago, Chile, 1994 S . Seshadri Computer Science Dept. IIT, Bombay 400 076 India seshadriOcse.iitb.ernet .in