Having read that the key technical concepts for SOA are services, interoperability, and loose coupling, you might conclude that all you have to do to enable SOA is to introduce services, interoperability, and loose coupling.
But as I stated earlier, you can't buy SOA. What's important is that you introduce these concepts in the appropriate fashion. That is, you have to find the right degree of centralization, you have to set up the corresponding processes, and you have to do your homework. A lack of these "ingredients" is what I most often find as the problem in real SOA projects. To establish SOA successfully, you have to care for your infrastructure, architecture, and processes (including the metaprocess, governance).
Infrastructure is the technical part of SOA that enables high interoperability. The infrastructure of a SOA landscape is called an enterprise service bus (ESB). This term is taken from enterprise application integration, where it was called the EAI bus or just enterprise bus.
The key feature of the ESB is that it enables you to call services between heterogeneous systems. Its responsibilities include data transformation, (intelligent) routing, dealing with security and reliability, service management, monitoring, and logging.
Chapter 5 will discuss the purpose and properties of an ESB in detail.
Architecture is necessary to restrict all the possibilities of SOA in such a way that it leads to a working, maintainable system. SOA ...