Taxonomy and formal properties of distributed joins

摘要

A general framework for studying the properties of joins between fragmented relations is presented. A join between fragmented relations can be performed as a set of partial joins between their fragments and can be represented as a join graph. A taxonomy of join graphs is developed. Rules are given for determining the class of a join graph from the properties of the fragmentation of relations and from semantic knowledge of different types of database dependencies. The fact that a join graph belongs to a given class is relevant for the efficiency of join execution; two typical application areas of these results are the design of distributed databases and the optimization of distributed queries.