Addressing Web Services Interactions

Vendor agreement on WS-Addressing spec paves way for richer interaction and improved efficiency.

I remember a poster in a college dorm room, back in the previous century, that said "I finally got it all together, but then I forgot where I put it." Information systems have historically been good at putting things together, and in their latest Web services incarnations theyve even gotten good at making things appear to be together without the burden of actually moving them around; until recently, though, IT systems have also made it difficult to figure out where things could be found. Perhaps were turning a corner with developments such as the WS-Addressing specification that was put forward last week by a team of authors from Microsoft, IBM, Sun Microsystems, BEA and SAP.

At first glance, its easy to dismiss WS-Addressing as merely a new formalism for something that people had already figured out how to do with extensions to URLs. As IBMs Doug Davis observes, one can always identify an instance of a Web service by appending something such as "?resourceID=123" to a URL, or by adding a SOAP header such as "<widget:resourceID>123

The endpoint references defined by WS-Addressing enable something more, though, because they provide a means of passing around references to Web services locations independent of the transport mechanism; the resulting conversations arent limited to a two-way exchange between a request point and a service point. Avanade Engineerings Steve Maine points out the implications, for example, for much more efficient implementations of multi-instance services with queues for handling requests and responses.

The Middleware Companys Steve Wilkes offers a more fully developed description of the opportunities to write "composite applications," saying: "Partner endpoints can be dynamically configured; all parties taking part in a process know how to relate messages to a particular process instance and each other."

Steve Eichert adds to Maines comments, saying, "Instead of limiting ourselves by always having our message response returned to the place that it was invoked from, we can introduce all kinds of flexibility regarding how the response is handled. We have the ability to chain web services together, and provide a dynamic pipeline for processing our message. WS-Addressing is cool."

Wilkes comments get an ironic seasoning from the fact that his former employer, AltoWeb, closed its doors just a little more than a year ago: Analysts at the time pointed to that closure as a sign of the consolidation that they felt was bound to take place in Web services vendors ranks. With major players such as IBM, Sun, Microsoft, BEA and Oracle offering complete software stacks, observers such as John Meyer of Forrester Research suggested that "Companies like M7, Bowstreet and others are going to have a hard time surviving in the future, especially when the other vendors have an entire stack to offer."

I hope that vendor-neutral, royalty-free mechanisms like WS-Addressing will make Meyer wrong about the loss of opportunity for smaller providers. With 75 percent of enterprises now estimated to be actively deploying Web services, buyers will be looking for vendors with domain expertise to give them an edge over those who merely purchase and deploy commodity technologies. With wireless and automotive platforms moving IT out into the real world, and not merely navigating around its own imaginary world, its important that IT providers with specialized experience be able to interface reliably with standards-based platforms.

Tell me what youll do when you know where your services are at

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