The U. R. strikes back

摘要

In this paper, we try to put to rest many of the objections to the universal relation concept that have appeared in the literature. First, we shall taxonomize the varieties of ideas that are sometimes called the "universal relation assumption." Then, we consider some of the arguments pro and con. In some cases, the arguments against were expressed prematurely, and solutions to the problems they expose have since been found. In other cases, the arguments against are simply fallacious. In still other cases, the problems pointed out are real, but simply serve to point out that the advantages of the universal relation are not gotten for free. We shall conclude the paper with a description of the algorithm used to interpret queries in System/U, and the reasoning behind it.