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Authors: Bradley, James
Keywords: Computer Science
Issue Date: 1-Apr-1984
Abstract: Non cyclic associations in relational data bases are classified into primitive and non primitive associations. A primitive association exists between a pair of relations if an association formula 0 holds, and involves only attributes from these relations. A non primitive association requires the association formula to involve attributes from intermediate relations in addition. Primitive associations comprise primary, secondary and generalized associations. Primary associations lead to FDs, secondary associations to embedded MVDs, and generalized associations to generalized dependencies. Non primitive associations comprise 1:n, n:m, and obscure associations. For any association class it is possible to define one or more association modes using either biconditional or implicational mode generators. Six types of associative conditions are defined on the basis of how associations are used in natural languages. Two types of associative conditions permit the use of natural quantifiers. SQL/N permits all six types of conditions. Association modes permit specification of any class of association with the associative conditions allowed in SQL/N. SQL/N is an extended version of SQL that is upward compatible with it. SQL does not permit all six associative condition types with any association.
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