What is SOA "in plain english"?

soa
Elena picture Elena · Jan 8, 2010 · Viewed 149k times · Source

Can someone explain in plain english what is SOA all about? I hear SOA here, SOA there but I cannot understand exacly what it is and what is used for. Was it some simple concept and later evolved into something huge or what?

All documents, including wiki are a bit abstract or maybe I'm an idiot and don't get it. Is there an idiot's guide on this?

What exactly is there behind these three letters?

Answer

Norman Ramsey picture Norman Ramsey · Jan 8, 2010

SOA is a new badge for some very old ideas:

  • Divide your code into reusable modules.

  • Encapsulate in a module any design decision that is likely to change.

  • Design your modules in such a way that they can be combined in different useful ways (sometimes called a "family" or "product line").

These are all bedrock software-development principles, many of them first articulated by David Parnas.

What's new in SOA is

  • You're doing it on a network.

  • Modules are communicating by sending messages to each other over the network, rather than by more tradtional programming-language mechanisms like procedure calls. In particular, in a service-oriented architecture the parts generally don't share mutable state (global variables in a traditional program). Or if they do share state, that state is carefully locked up in a database which is itself an agent and which can easily manage multiple concurrent clients.