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
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