The bottom line with XML is that it is just structured text. The power of XML lies in the fact that it pretty much allows any computing platform and language to process text. Add that to the fact that XML was created as a mechanism for the creation of application specific data structures, and we have a great mechanism for exchanging data between systems.
Communication within modern SOA takes place using Web services. To implement them, we need to provide a set of protocols and formats to convert our abstract SOA triangle into a concrete implementation. To do this, we need: