Sunday, May 11, 2008

REST Notes

These are links and notes from various sites about REST architectural styles.

Q: Can you elaborate a little on why you think these would be tightly coupled? I mean everybody is talking about loose coupling and SOAP

A: I miss that one. When I was selling Systinet's products I talked about loosely coupled, when I present information for Burton Group on SOA I certainly stress "Trying to do your best to loosely couple client to server", because obviously loose coupling is a very good idea. The issue and I have said this before in print, is that you can strive for the largest amount of loose coupling possible in the SOAP WS-* world, and when you do the best job possible and when you obey all the best practices, you still end up with a tightly coupled system.

And you know the answer, but for the audience out there the fact of the matter is when you are creating a SOAP web service, a client, you have to know a great deal about that service, whether you learnt it via WSDL or some other mechanism, you have to know a great deal about it, and generally if the service changes in any not even terribly significant way, your client has to change with it or it will simply stop working. And you can go through heroic efforts to keep the existing clients alive and you can try and do your best at the design and development phase to loosely couple them, but the fact that the client has to know all the operation names and all the message formats before it can get any value out of a web service, is tight coupling to me.

Where of course in contrast all I need to know about a RESTful web service is its URI. Now I might not be able to derive all of the business values that the service can offer, but I can "GET" it and maybe something interesting will come from that, and it may be all the information I need. So properly designed RESTful system is dramatically loosely coupled, whereas a properly designed SOAP WS-* based system is unfortunately tightly coupled and all you can do is your best effort to avoid more tightly coupling than necessary.

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