SOAP vs. POX vs. REST says -
So if you want security, reliability etc., you need SOAP (or you have to invent your own version of it and convince others to use it too .. good luck). Obviously not every scenario needs all that muscle ...
POX/HTTP means exchanging plain old XML documents over HTTP. RESTful POX, i.e. using XML in a RESTful manner, would mean POX is a subset of REST. Many, if not most POX applications don't care about REST very much, though � they'd thus be part of a distinct set of applications.