## function

<*mathematics*> (Or "map", "mapping") If D and C are sets
(the domain and codomain) then a function f from D to C,
normally written "f : D -> C" is a subset of D x C such that:

1. For each d in D there exists some c in C such that (d,c) is an element of f. I.e. the function is defined for every element of D.

2. For each d in D, c1 and c2 in C, if both (d,c1) and (d,c2) are elements of f then c1 = c2. I.e. the function is uniquely defined for every element of D.

See also image, inverse, partial function.

<*programming*> Computing usage derives from the mathematical
term but is much less strict. In programming (except in
functional programming), a function may return different
values each time it is called with the same argument values
and may have side effects.

A procedure is a function which returns no value but has only side-effects. The C language, for example, has no procedures, only functions. ANSI C even defines a type, void, for the result of a function that has no result.

Last updated: 1996-09-01

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**Nearby terms:**

**function**» functional » functional database » functional dependency