Idempotent
Went through a great MSFT Presentation [again...]. Gotta like those presentations.
Came across a word: Idempotent. Actually this word is used very much in mathematical circles and even in the DBA Circles.
[Technical Definition]
Idempotent = relating to or being a mathematical quantity which when applied to itself under a given binary operation (as multiplication) equals itself; also : relating to or being an operation under which a mathematical quantity is idempotent.
In other words,
[Layman Definition]
If X is idempotent, that means that
1) Multiple effects of X is the same as a single effect of X
OR
2) X is unique on its own and cannot be replicated.
Therefore, you can always say that a credit card transaction or a billing transaction should be and is Idempotent (in a management meeting and watch jaws drop...) to prevent double billing or charging...
The DELETE in CRUD should be designed to be Idempotent as well...
I believe you will see this term more as Reliability in Messaging (WS-ReliableMessaging) gains momentum and acceptance in the future.