I have been hooked up to REST these days after having some times to go through the WCF Web Programming Model (I know I am lagging behind in technologies !).
While looking at the pros and cons of REST and WS-*, I could see more then few web pages, blogs, on the debate of what’s the best solution for SOA.
REST is easy to use, no SOAP-client tool kits needed to generate web service proxies, as the fundamental concept behind REST being every operation is accessed by its unique URI, it's just a matter of typing it in your web browser, this also makes testing easier for developers (as all they need to do to see if the service is working, is to type the url in the browser !)
Further more if your are practicing an asynchronous pattern such as using AJAX, it might be very easy to call a REST service, get the response in JSON and do the processing on the client side, this is much easier then using the typical DOM method to parse XML.
When it comes to coupling, REST is more loosely coupled then WS-* services, because with WS-* web services, the client needs to know a great deal about the service and if the web service changes, your client need to update for it to continue working, but with REST, your only need to know the URL of the resource and nothing more, this makes REST more loosely coupled then WS-* web services.
From the non-functional requirement point of view, simplicity of architecture, performance due to no or less XML overhead and caching of result set (page) which is
built into the back bones of HTTP and the ability to server a huge number of clients due caching and clustering support built into REST (HTTP), stand out.
This does not mean WS-* or SOAP web services are going away...WS-* web services from my opinion are the best choice for enterprise applications (although there is a debate to this), with it's reliability, security and transactional capabilities.
REST does not support distributed transaction directly, and when it comes to security, REST has to entirely depend on the best it has, SSL.
REST would always be a better choice when it comes to developing services when you don’t know your clients, in other words the type of clients. As a final point, it’s is very clear that when it comes to WS-* web services, there are more alternatives when it comes to making architectural decisions and if advanced functionality delivered by WS-* is needed, it is no easy thing to extend RESTful services to deliver this
So finally to say, I am not saying REST is better then SOAP or vice versa, but what I am saying it's a matter of
pure architectural decision.
This is not a compressive comparison between REST and WS-* but instead a snap shot.