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The Relational Database Dictionary, Extended Edition by C. J. Date

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Chapter 14. M

managed redundancy Controlled redundancy, q.v.

mandatory participation See cardinality constraint.

many-to-many correspondence Strictly, a rule pairing two sets s1 and s2 (s1 and s2 not necessarily distinct) such that each element of s1 corresponds to at least one element of s2 and each element of s2 corresponds to at least one element of s1; equivalently, that pairing itself. Often used loosely, however, to mean a pairing such that either (a) each element of s1 corresponds to any number of elements of s2 (possibly none at all) and each element of s2 corresponds to at least one element of s1, or (b) each element of s1 corresponds to at least one element of s2 and each element of s2 corresponds to any number of elements of s1 (possibly ...

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