## relation

1. (mathematics) A subset of the product of two sets, R : A x B. If (a, b) is an element of R then we write a R b, meaning a is related to b by R. A relation may be: reflexive (a R a), symmetric (a R b => b R a), transitive (a R b & b R c => a R c), antisymmetric (a R b & b R a => a = b) or total (a R b or b R a).

See equivalence relation, partial ordering, pre-order, total ordering.

2. (database) A table in a relational database.

Last updated: 1995-02-28

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