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Download Dependencies in Relational Databases by Prof. Dr. Bernhard Thalheim (auth.) PDF

P(v,, ••• ,vn)) where if A~ = Ck and Bk = A, for some k X~ u~ { otherwise if A~ - Bk for some k if A~ - Ck for some k and for no 1 B1 • A~ v~ • Y~ otherwise z. satisfies X@Y if for any tuples t , t' from r if t(C~) • t'(B~) for i , 1~1~m , then there exists a tuple t" such that t"(B~) • t(Bo) for i, 1~i~m, and t"(C~) = t'(C~) for i, 1~i9a The closure dependency can be understood as a constraint which states that the relation is obtained by its transitive closure on X and Y • For closure dependencies there is necessary only one inference rule for the 1mplication of { X@Y } i= Y@X .

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