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WOA: Putting the Web Back in Web Services

by Nick Gall  |  November 19, 2008  |  17 Comments

As my friend and colleague Anthony Bradley just pointed out in his blog, our WOA note has finally been published (subscription required) and it’s something that I am very proud of. Not just because my co-authors Anthony, Dan Sholler and I produced a well-crafted piece of research (if I do say so myself), but more importantly because we built consensus in support of Web-Oriented Architecture across Gartner over the past several years.

Because of such consensus, the note can put forward Gartner positions such as:

  • Interfaces based on WS-* specifications should be constrained by WOA, especially the generic interface constraints.
  • More often than not, the WS-* protocol toolkit is unconsciously misused to create needlessly specialized interfaces.
  • Application neutrality should be the principal goal of an interface, and implementation neutrality should be a secondary goal.

While I can’t share the entire note with the blogosphere, I can share a couple of highlights — first and foremost the official Gartner definition of Web-Oriented Architecture:

WOA is an architectural substyle of SOA that integrates systems and users via a web of globally linked hypermedia based on the architecture of the Web. This architecture emphasizes generality of interfaces (UIs and APIs) to achieve global network effects through five fundamental generic interface constraints:

  1. Identification of resources
  2. Manipulation of resources through representations
  3. Self-descriptive messages
  4. Hypermedia as the engine of application state
  5. Application neutrality

Those of you familiar with Roy T. Fielding’s REST Thesis will no doubt recognize that WOA’s five generic interface constraints are an extension of Roy’s four uniform interface constraints. The one additional constraint, application neutrality, is implicit in the thesis, but we think it is so fundamentally important that we made it a "first class" constraint.

What is application neutrality? Here is a brief excerpt from the 13-page report:

The primary problem with the specifications known as WS-* (such as SOAP, WSDL and UDDI) is that their principal emphasis is on implementation neutrality. All the specifications focus on generalizing away the details of specialized middleware technologies, so that services can be accessed using any one of those technologies. Although this is not an unworthy goal (especially for vendors of specialized middleware technologies), it shifts the focus from the generic interface constraint of application neutrality.

Application neutrality should be the principal goal of an interface, because it is precisely this characteristic that enables shareability (a fundamental SOA principle). In other words, interface designers’ primary goal should be generic, application-neutral interfaces, which generalize away application-specific details.

The key to shared use (reuse) is a generic, application-neutral protocol, such as the Atom Publishing Protocol (APP) or Google’s GData Protocol. Conversely, the more application-specific a protocol is, the less shareable it is. With sufficient generality, the most powerful kind of reuse becomes possible: serendipitous reuse. So important is this kind of reuse that Tim Berners-Lee and Roy T. Fielding have highlighted it an essential characteristic of the Web:

  • "Unexpected reuse is the value of the Web" (Tim Berners-Lee)
  • "Engineer for serendipity" (Roy T. Fielding)

In terms of Gartner’s hourglass model for identifiers, formats and protocol operations (IFaPs), application neutrality makes the top of the hourglass wider; implementation neutrality makes the bottom wider. A wide top is more important than a wide bottom. In other words, generic application protocols (application neutrality) at the top of the hourglass are more important in creating powerful network effects than portable implementation protocols (implementation neutrality) at the bottom of the hourglass.

The key to generic interface design, WOA-style, is nested generality: gradually specializing generic interfaces in small increments. Whatever level of generalization one begins at — whether it is at the APP-envelope level or the SOAP-envelope level — it is a mistake to embed application-specific schemas and identifiers in either envelope.

Don’t just build on generic interfaces; build up generic interfaces that are only slightly less generic than those built on.

One last point highlighted in the note: let’s not get into a battle over names. If you don’t like the name WOA, call it REST, or ROA, or Web Architecture, or Fred. "The goal is to focus on the key generic interface constraints that unite these concepts, not debate the nuanced differences among them."

We’d love to hear your feedback on this key set of concepts –especially application neutrality — whatever name you choose to call it!

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Category: gartner  soa  woa  

Nicholas Gall
VP Distinguished Analyst
14 years at Gartner
35 years IT industry

Nick Gall is a vice president in Gartner Research. As a founding member of Gartner’s Enterprise Planning and Architecture Strategies, Mr. Gall advises clients on enterprise strategies for interoperability, innovation and execution. Mr. Gall is a leading authority on middleware… Read Full Bio

Thoughts on WOA: Putting the Web Back in Web Services

  1. As a long time enterprise architect, I have to say that the implications of this research will be far-reaching.

    Not only for enterprise architects or application developers, but for the traditional end-user, this signals a paradigm shift in thinking about the composition or orchestration of a solution. Imagine a set of application neutral generic interfaces that end-users link together for purposes they discover at the point in time in which they wish to create the solution to their problem. This infers that the solution has not been woven together for them before they think about the problem they wish to solve. Of course, this does not mean that someone in the finance department is going to compose a new order-to-cash solutoin tomorrow. But, it does foreshadow things to come.

    For EA vendors, this changes the nature of state management and, potentially, the role of enterprise architects as well.

    Personally, it’s exciting to work off of such insightful research (okay, I’m publically slapping my colleagues Nick, Dan and Anthony on their backs).

    I’ll be speaking about this as part of my keynote at the EA Summit in Las Vegas, December 10-12, on “…The Present and Future of Enterprise Architecture”. With Malcom Gladwell, author of both “The Tipping Point: How Little Things Make a Big Difference,” (2000) and “Blink: The Power of Thinking Without Thinking” (2005), at the conference, it will definitely make people sit up and think about how this will, and when this will, impact their world today.

    Coming straight off of the co-located Gartner Application Architecture, Development & Integration Summit, I’m certain that the opportunity to meet you, Nick, as well as Anthony and Dan regarding this seminal work will be a great opportunity for those who can tear themselves away for a week in Vegas this December.

    If I could recommend one read this year, this note is it.

  2. Mike Bergman says:

    Congratulations! I’m still seeing where I can scrape up the pennies to purchase this report.

    I believe this advocacy to be critically important. As you continue to evangelize, however, please do try to keep the linked data part (see your post integrated with the WOA vision as well.

    As I pointed out in a recent piece (, the combination of RESTful services and data points to a very adaptive and powerful architecture for enterprises and all organizations.

    Please do keep posting snippets from your note so that those of us still gathering the pennies can glean the important points.

  3. Anthony Bradley says:

    I like that you highlighted Application Neutrality in the segments you posted. You appropriately talked about the shareability it can deliver but I would also like to emphasize that without AN there would be no Web. Imagine how large the Web browser would need to be if it had to execute millions upon millions of unique “operations” associatd with specific Web pages. The generic HTTP verbs GPPD are mandatory for basic Web function … but the real kicker is that AN is what drives the adaptability and evolvable (i.e., agility) aspects of the Web. This is the best kind of serendipity. Since agility is one of if not the major goal of SOA, I wanted to articulate AN in those terms.

    We really should see if we can open up this note to the public. As Phillip said, it has far reaching implications and the term WOA is catching on. We really don’t want 800 definitions of WOA surfacing and causing confusion. Let’s see if this blog generates some demand.

  4. […] just read Nick Gall’s post WOA: Putting the Web Back in Web Services.  The whole notion of Web Oriented Architecture (WOA) is to leverage the basic web concepts from […]

  5. […] du moment : Representational State Transfer (REST) et Web Oriented Architecture (WOA) (Cf. Gartner – WOA: Putting the Web Back in Web Services ou Burton Group : The Tao Of REST), sans oublier les promesses mirobolantes du Software As A […]

  6. […] 말처럼 WOA의 5가지 인터페이스 제약 중 처음 4가지는 REST의 단일 인터페이스 […]

  7. […] recent post by Nick Gall of Gartner on WOA: Putting the Web Back in Web Services stirred up some interesting buzz. This post presents Gartner's definition of […]

  8. […] WOA: Putting the Web Back in Web Services (tags: woa web roa rest http architecture gartner) […]

  9. […] – I agree with Ian’s view that this isn’t really appropriate for the Web. RMR, ROA or WOA (take your pick!) is a much better fit. Having said that, I’m not sure how much the developer […]

  10. […] most important aspect of WOA is application neutral interfaces (or as some prefer application generic interfaces). Since […]

  11. […] it.  Now do you recognize him? It’s the guy who read up on Web Oriented Architecture because Nick Gall or Tim Berners-Lee said it would be hot. It’s the woman who studied all night to learn the […]

  12. […] that it took less than three hours to create this.  It just goes to show that if you follow basic WOA principles, the ability to compose new capabilities is amazingly quick for a very broad potential […]

  13. […] "Web-orientation is a prerequisite for rapid integration of data and business processes; it enables situational development models, such as mashups; and it’s the foundational architecture for SaaS and cloud computing." […]

  14. […] For anyone confused, this announcement appears to be for W.S SOA. His Restful Cousin, who sometimes goes by the nickname WOA, is alive and well. […]

  15. […] promises, largely because of the calcifying impact of the WS-* stack, putting forward Nick Gall’s Web Oriented Architecture (WOA) as an alternative. Burton’s Anne Thomas Manes recently declared SOA dead, although to be […]

  16. […] the Snowflake APIs by Bill de hÓra which reminded me of an older post by Nick Gall from Gartner on WOA and the need for application […]

  17. […] some have variously said SOA is Dead, or we need to rethink everything and move to Web Oriented Architecture… IBM had just pragmatically introduced the notion of RESTFUL SOA. Why not just integrate […]

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