idempotent

idempotent

Refers to an operation that produces the same results no matter how many times it is performed. For example, a database query that does not change any data in the database is idempotent.

Functions can be designed as idempotent if all that is desired is to ensure a certain operation has been completed. For example, with an idempotent delete function, if a request to delete a file is successfully completed for one program, all subsequent requests to delete that file from other programs would return the same success confirmation message. In a non-idempotent delete function, an error would be returned for the second and subsequent requests indicating that the file was not there.

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idempotent [¦i‚dem¦pōt·ənt]

(mathematics)

An elementxof an algebraic system satisfying the equationx²=x.

An algebraic system in which every elementxsatisfiesx²=x.

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1.		idempotent - A function f : D -> D is idempotent if f (f x) = f x for all x in D. I.e. repeated applications have the same effect as one. This can be extended to functions of more than one argument, e.g. Boolean & has x & x = x. Any value in the image of an idempotent function is a fixed point of the function.
2.		idempotent - This term can be used to describe C header files, which contain common definitions and declarations to be included by several source files. If a header file is ever included twice during the same compilation (perhaps due to nested #include files), compilation errors can result unless the header file has protected itself against multiple inclusion; a header file so protected is said to be idempotent.
3.		idempotent - The term can also be used to describe an initialisation subroutine that is arranged to perform some critical action exactly once, even if the routine is called several times.