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Posted by Abel Avram on Jan 30, 2009
In this presentation recorded during QCon London 2008, Stefan Tilkov introduces the audience to REST seen as an architectural style. He thinks that REST is not an alternative to SOA but it can serve SOA to reach its goals. Stefan also covers other related topics: HTTP, WS-*, SOAP, CORBA, RPC, enterprise, in an attempt to make the listeners understand what REST is and what is not and how it helps.
Watch: REST: A Pragmatic Introduction to the Web's Architecture (1h)
Stefan offers three SOA definitions:
Stefan continues with three definitions of REST:
Following, Stefan takes the second definition, REST-ful HTTP, and explains it:
Stefan continues by explaining how to design a good RESTful application and gives a simple example using pseudo-code. He also presents some of the features and advantages HTTP has, and talks about HTTP, REST, SOA, WS-*, Internet, enterprise for the rest of the session which is concluded by Stefan taking questions from the audience.
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This is probably the first comparison of REST Vs SOA, WS.*, SOAP that explains how they can be compared.
It would be interesting to get Stefan's opinion of Ross Altman's latest presentation. Ross is one of Sun's CTOs (for Business Integration) and he explains:
Assumption: RESTful Web services should be used instead of WS-* Web services
A case can be made for the use of RESTful services for Opportunistic applications. However, for Systematic applications, the Qualities of Service that are required would have to be built on an ad hoc basis.
As a result, the cost of RESTful services would go up and interoperability would go down
If the counterparties building a RESTful interaction have to “reinvent the wheel” of runtime governance standards, the costs and complexity of RESTful Web services would increase dramatically, undermining the attractiveness of the REST model
Since the runtime management capabilities for each RESTful Systematic application would be developed in a non-standard way, interoperability between RESTful implementations would drop drastically
When do you think we can throw darts at REST-*?
As you're asking for my opinion: No, I don't believe that WS-* will have to be re-invented for RESTful HTTP. For example, I believe that there are many, many more opportunities for runtime governance of RESTful HTTP services already, as the infrastructure has much more visibility into the messages flowing through it.
Hum... so if we take the elements of Runtime Governance for instance:
- registry / repository
- policies
- security
- change management
- event management (as in Incident / Problem resolution)
Could you explain how these pieces work in REST since there are no contracts, no boundaries, no policies, no agreed upon versioning capability, URIs are bolted on resource access operations (making it hard to deal with Change) and finally, how do you go about conducting a root cause analysis across a domain that has no autonomous boundaries (i.e. where the only explicit boundary is the network authority that owns a particular URI).
When you build a Web App, you can monitor if it's up or down, and how it is behaving. When you cover a network authority with a series of "resources" where do you start when an event/incident/problem occurs? You go straight back to the design doc? you have no impact analysis capabilities?
Sorry for noting your comment so late.
1) Are you suggesting there are widespread runtime governance standards for WS-*? Like what? UDDI? Currently, every governance product uses its own proprietary approach.
2) You are free to use XML Schema, as much as you want to, when using RESTful. If you want to base part of your governance on the evolution of schemas, nothing stops you.
3) There is no versioning support in WS-* that I'm aware of. The stuff I've read about it (including yours) talks about options for XML Schema versioning, which IMO a) still sucks b) is available for REST/HTTP if you disagree
4) While I've seen tons of articles and presentations discussing the use of policies for governance, I've never seen it applied in practice.
5) The impact analysis support I've seen in governance product requires additional metadata that has to be explicitly added, such as usage relationships between consumers and providers. This seems to be entirely orthogonal to the REST vs. WS-* discussion in my view.
6) I fail to see how URIs make it hard to deal with change - in fact I disagree strongly. They offer a workable means to support old, new and unknown clients that I've not seen in the WS-* world.
7) How are incident management and REST/WS-* related?
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