1. Communications

In SOA, both the W3C and OASIS versions, all communications between services are carried out by message exchange. These messages are XML documents, generally carried by the HTTP protocol (but which could also be carried by other protocols such as SMTP). To implement these exchanges as widely as possible, it was necessary to find a way of modeling in XML the addressing, routing and correlation information between messages, etc. that is essential to the smooth running of a messaging system. The W3C has standardized a large number of XML specifications, often initially proposed by computer industry players – Microsoft, Sun and IBM, all three very active in this role –, and which have become indispensable for deploying a form of XML "middleware" for Web services-based applications.

XML is used at two distinct levels in the SOA infrastructure. On the one hand, the content...