Abstract
The present paper deals with an important problem of the relational database theory, with analysis of dependencies. In the first part of the paper it is shown, that a sufficiently large class of dependencies (“hypothesis - conclusion” type of dependencies) can be expressed as first-order sentences. In the second part of the paper we deal with implication problems for EGD, TTGD, TGD types of dependencies of relational databases, wich are generalizations of dependencies, introduced by Beeri - Vardi ([2]). For these implication problems we give a generalized version of the proof procedure called chase. We introduce exchangeability-generating dependencies (XGD) and analyze the structure of relational database classes satisfying a system of XGDs, (EX).
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