Idempotent methods are one which returns the same result. For example multiply(a,b). The method does not have any side effect. The HTTP GET methods method is supposed to be idempotent whereas POST is not.
Yes. Mathematically,if R is some set and if it holds Associative/distibutive/closure properties and if some element x of R has the property such that x*x = x then element x is said to be idempotent. For example ,any square identity matrix should be idempotent. [ September 30, 2005: Message edited by: Arjunkumar Shastry ]