IETF: The HTTP Query Method ( Draft)
> QUERY requests are both safe and idempotent with regards to the resource identified by the request URI. That is, QUERY requests do not alter the state of the targeted resource. However, while processing a QUERY request, a server can be expected to allocate computing and memory resources <i>or even create additional HTTP resources through which the response can be retrieved</i>.<p>The possible creation of extra HTTP resources (response resorces?) seems to me contrary to idempotency. That seems more like the territory of POST.<p>If two identical QUERY requests might produce different response resources, how to square that with the the fact that QUERY will be cacheable?