There the idea is everything in the system is services, so the communication between service happen using message passing. So system become so flexible and extensible. And there are few ways of implementing SOA too;
- Using existing messaging system
- POX- Plain Ole XML
- Web services
And I think Web services became very success in the SOA, and it has become a industry stranded for SOA. So many specification, so many implementation. Above all due to standards and standards bodies like WSI, most of the implementations are said to be inter operate. For example Microsoft .Net and Apache Axis2 inter operate each others.
Moving beyond the service oriented architecture, now people are developing system using building blocks called components. With the introduction of OSGi it has become a very popular topic. When I heard about OSGi I did not realized the power of OSGi and specially components based systems. But now I know the power. Even Axis2 can be used as an OSGi bundle (or component).
By adopting to the new technology WSO2 has also moved most of its projects to OSGi based components, as a result of that they can build different kind of system integrating different building blocks of OSGi bundles. By looking at the activities going on, I would say WSO2 Carbon is becoming one of the coolest project or rather framework for building SOA related technologies, such as Web Services, ESB, Registry etc, ..