Wednesday, December 12, 2007

Why Is REST (Seen To Be) Simpler Than SOAP-Based Web Services?

I had these points under another post earlier, but they really deserve their own post.

I really don't believe there is a huge difference between SOAP and REST or that there is a "war" between them. Yes, REST has been much simpler and more elegant than SOAP-based Web Services so far, but why do you think that's so? This is a multiple-choice question.

(a) There's still some basic confusion in the REST camp and elsewhere between SOAP messaging (the modern model of SOAP) and SOAP-RPC (the outdated view). What RESTafarians attack is the now-universally condemned SOAP-RPC model.
(b) The scope of SOAP/BPEL being much more than that of REST (Message Exchange Patterns, Qualities of Service, Processes, to name a few), the WS-* standards are understandably richer and more complex. As REST begins to move beyond the low-hanging fruit it currently targets, it'll get complex too.
(c) The vision of SOAP messaging hasn't yet been completely translated into reality - e.g., nominally transport-independent but still has no transport bindings defined other than HTTP, the unnecessary WSDL abstraction of "operation" rather than "message" as the basic primitive. Rumblings around AMQP and SSDL provide hope that the vision may yet find more optimal implementations.
(d) WS-* Standards bodies are political menageries. The spec writers have made things more complex than they need to be. Future iterations will shake out the bad specs.
(e) Things are actually settling down in the WS-* world. The core specs are done and dusted (WS-Addressing, WS-Security, WS-SecureConversation, WS-Trust, WS-ReliableMessaging). Implementations are much more interoperable. Tooling has improved. Policy-based configuration of services is becoming a reality (WS-PolicyFramework, WS_SecurityPolicy, WS-ReliableMessagingPolicy). A Tango demo will blow you away.
(f) All of the above.

I believe the answer is (f), which means that the REST folk can stop crowing. There's a place in this world for SOAP (SOAP messaging, that is), and it's right up there alongside REST. Neither is "superior". (In fact, both have areas for improvement, but I'll go into that in another post.)

Forget all the issues around complexity. I believe that in time, complexity will cease to be a differentiating factor between WS-* and REST. What will be left are two equally valid ways of looking at the world, and SOA practitioners will choose the view that is appropriate for the task at hand.


u said...

Agreed on the "horses for courses" approach with SOAP vs. REST.

However I am not in agreement with you in regards to concluding that REST will become just as complex as SOAP.

The basic premise of REST lies in the simplicity and atomicity of its approach. If someone creates a complicated Resource Oriented Architecture (ROA) then they are missing the point and frankly, using the wrong approach.

SOAP-Messaging is where you need to go if you see your architecture evolving into complicated message exchanges with multi-boundary contexts and a need for consistency.

Just my two cents...



Arun Gupta said...

See Tango demos at: