[4] UserLand supported XML-RPC from version 5.1 of its Frontier web content management system,[4] released in June 1998.
[6] Prior art wrapping COM, CORBA, and Java RMI objects in XML syntax and transporting them via HTTP also existed in DataChannel's WebBroker technology.
[7][8] The generic use of XML for remote procedure call (RPC) was patented by Phillip Merrick, Stewart Allen, and Joseph Lapp in April 2006, claiming benefit to a provisional application filed in March 1998.
In comparison to RESTful protocols, where resource representations (documents) are transferred, XML-RPC is designed to call methods.
The practical difference is just that XML-RPC is much more structured, which means common library code can be used to implement clients and servers and there is less design and documentation work for a specific application protocol.