Definition and Analysis of Index Organizations for Object-Oriented Database Systems

Abstract The efficient execution of queries in object-oriented databases requires the design of specific indexing techniques, to efficiently deal with predicates against nested attributes or against class inheritance hierarchies. Indexing techniques so far proposed can be classified into three groups: inheritance indexing techniques, whose goal is to support queries along inheritance hierarchies; aggregation indexing techniques, dealing with the efficient evaluation of nested predicates; integrated techniques. The aim of this paper is to analyze two techniques providing an integrated support, the path index and the nested-inherited index, with respect to traditional techniques, such as the multi-index and the inherited multi-index. The analysis is performed assuming that multi-valued attributes, as well as instances with null attribute values, are present in the database. For this purpose, the paper first presents the considered techniques. An extension of the path index, firstly defined in [6], is proposed to deal with multi-valued attributes and instances with null attribute values. Then, an analytical cost model for the extended version of the path index is presented. The cost model is finally used, together with the cost models presented in [2], to compare the various index costs, with respect to storage, retrieval, delete and insert operations. The results show that traditional techniques have better performance with respect to storage, delete and insert costs, whereas integrated techniques have lowest costs for retrieval.