Service Oriented Architecture is an umbrella term very similar to that other umbrella term, “web services”. SOA refers more to how these web services interact, however, in a system. Below is a diagram I’ve knocked up which shows in a very crude fashion the difference between traditional models and SOA.
I hope this explains it a little… frankly, some of the diagrams out there that are supposed to explain SOA simply look like someone’s eaten a technical dictionary, felt ill and thrown it all up.
I’ve explained SaaS and DaaS in some detail in this blog. We’ll talk about PaaS later. Expect this diagram to pop up again when I do.
You can reproduce this simple diagram wherever you like so long as you give a little attribution by linking back to this blog.
Edit: here’s a more detailed description of Service-Oriented Architecture.