On the optimal top-down evaluation of recursive queries

Abstract

In this paper, we present a top-down but set-oriented method for handling recursive queries. Based on the RQA/FQI's mechanism for recording "path information" [14], we try to eliminate many of the expansion operations that have to be done by any other top-down strategy. Further, we speed up the evaluation for cyclic data by generating most answers to a query directly from the intermediate results and the relevant path information instead of evaluating them by performing algebraic operations. In this way, high efficiency can be achieved. On one hand, the search space becomes smaller in our method. On the other hand, the cost of generating an answer is much less than that of evaluating an answer by algebraic operations or by other standard methods.