what is idempotent
One of the important aspects of REST (or at least HTTP) is the concept that some operations (verbs) are idempotent. As Gregor Roth said several years ago: The PUT method is idempotent. An idempotent method means that the result of a successful performed request is independent of the number of times it is executed. Idempotency is also something discussed in the SOA Design Patterns.