XMLRPC

SOAP should be used instead whenever possible. There is unconfirmed rumor that it has a license problem.

For more information see http://www.xmlrpc.com/

Some reasoning: the spec reveals a taste of illiteracy about xml. Too much tag nesting, type information is clearly somthing with ought to go into attributes, xml expresses per definition structure, thus structure ought to be tagged with xml tags of corresponding name, not an element named 'member' with subelements named 'name' and 'value' etc. Sure this has the advantage that it's easy to check the rcp call itself agains some dtd or scheme, but that's just an extra round of checking since the real check is going to be on the final structure.