WOA and "Application Neutrality"

A 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 WOA:

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

This is essentially a rehash of REST except for the fifth point on "application neutrality". Nick explains this further.

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.

This is intriguing. How can you generalize away application-specific details from the interface, and yet do something meaningful and concrete? Nick goes on to illustrate this.

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.

This still did not make sense to me. In particular, APP and GData are profiles of HTTP, and not new application neutral protocols. After some back-and-forth discussions on the REST-discuss list, it turned out that "application neutrality" meant using generic media types such as the Atom Syndication Format for representations. Now, this is something I can comprehend.

So is WOA = REST + generic media types? It was not very clear from his post, but that seems to be the the gist of this definition. Using media types such as HTML, XHTML, and Atom makes sense in some cases, but saying that it should be the goal of an interface to use such media types is a stretch. Media types should be able to convey the type of representation, and by using generic types, applications lose describability.

It is unfortunate that Gartner chose a vague term like "application neutrality" to describe this. But on the positive side, they are at least talking about REST.

Tagged as: REST