Composition of database relations

The authors argue for implementing composition as a primitive operation and present a single-sided composition algorithm that performs join protection and duplicate elimination as one unified operation. They report experimental results that show an operating region in which this algorithm outperforms composition by the standard method. This operating region is characterized by a join result many times larger than the source relations, and many duplicates after projection over the nonjoin attributes. This occurs, for example, in deductive databases when computing transitive closures of dense graphs