Operation-oriented query language approach for recursive queries—part 1. Functional definition

摘要

So far the aspects related to efficient processing have dominated the research on recursive queries. In this paper we consider how the formulation of recursive queries can be made easier from the view point of the non-professional user—also in the context of complex recursive queries. It is obvious that the conventional rule-based way of defining is too hard and cumbersome for many non-professional users. We provide operations at a high abstraction level in terms which the user can formulate his recursive queries in a compact and convenient way. In our approach recursive processing is needed for constructing transitive relationships among data. In practice, it is often very important to compute transitive relationships among several union-compatible binary relations instead of one binary relation as usual. We define the operations so that they are able to manipulate transitive relationships among several relations. For the changing needs of the user our approach contains three kinds of operations: relation-oriented, node-oriented and path-oriented operations. In this paper we specify a functional language consisting of operations of these types and give several examples on how the user can formulate his recursive queries in terms of this language. We also discuss its role in deductive databases, i.e. its integration with processing based on an extensional database.