The Relationship between Dependency Classes

In the previous chapters, more than 80 different dependency classes are introduced and considered. In /THAL 86/, more than 600 different references to papers on dependency theory are given. By some authors it was noticed that dependency theory is in a chaotic state. This book should be understood as an attempt to present the most important results on dependency theory. The usefulness of such a great number of different constraints is an open problem. But the variety can be explained as follows: 1Each new type represents a certain type of semantic constructions.2Many types are connected with normalization and decomposition theory of databases.3Some types are generalizations of the previous ones.4Some types are introduced as special tools for manipulation and control of data.5Some types improve the utilization of projections of relations or of partition of relations.