Extended Conditions for Answering an Aggregate Query Using Materialized Views

A view is a virtual relation defined in terms of ba se relations and is said to be materialized if it is stored in the database. In the past few years, mate rialized views have attracted a significant amount of research in many applications environments as a means of enhancing query performance. Materialized views offer significant performance ad vantages in evaluating a query by eliminating the need for recomputing the views. Just as a cache , a materialized view is a type of replicated copy of information derived from base relations and, hen ce, the technique is very useful in various applications where access to local or cached views may be cheaper than access to the base relations. Although many approaches for utilizing materialized views in evaluating a query have been proposed [1, 2, 4, 5], there were several restricti ons in selecting such views. First, only views whose relations are contained in those of a query w ere considered. Thus, if a view refers to relations not mentioned in the query, it was excluded from consideration. Furthermore, a view is also excluded if it does not contain the necessary attributes for the query. However, there are many cases where a view can be utilized even if the abov e restrictions are not satisfied. In this paper, we propose a new approach to using m aterialized views in answering an aggregate query. We extend the practical scope of utilizing m aterialized views which include those that would have been excluded in previous approaches. We first show the conditions for testing whether a materialized view can be utilized in answering a qu ery even if the materialized view has relations not mentioned in the query. These conditions are then extended by introducing a method that recovers the missing attributes. All conditions are designed to be applicable for ba g (multiset) semantics. Bag semantics are used in the underlying models of most practical database management systems.