TEAM Zarate Tarrani Notes From the Field

Dimming Light. Kate Hartshorn has taken an indefinite leave of absence from contributing her insights and thoughts here. Her time and efforts have been redirected towards a difficult, but surmountable, challenge. Until her return this weblog and its Postcards from the Revolution sister will be bereft of rare points of view and a touch of humor and class that is missing from most technical resources. When she does return it will be on a permanent basis.

Shedding Light. What are web services, and why is there so much debate about a definition? I subscribe to a large number of news services and this question arises, debate ensues, issues become murky and the process repeats itself. I go with the definition that is set forth in the W3C Web Services Architecture Requirements that states:

A Web service is a software application identified by a URI, whose interfaces and binding are capable of being defined, described and discovered by XML artifacts and supports direct interactions with other software applications using XML based messages via internet-based protocols.

That wasn't too difficult. We have a definition that is sanctioned by an internationally respected body, and until a better definition comes along why not go with it? It certainly cuts through the hype spewing forth from Microsoft, Sun and the industry experts.

If you're interested in web services architecture the following resources are essential reading:

• W3C Web Services Architecture Working Group. Yes, the W3C is a politically-charged organization, but they are respected and set standards to which the squabbling factions (a.k.a., Oracle, Microsoft, Sun, etc.) pay close attention. Ignore their standards and what is happening within their working groups at your peril. It's also interesting to note that the W3C cites the Architecture Trade-off Analysis (ATAM) approach supported by the Software Engineering Institute as an influence. I have a few papers on ATAM in the December 2000 issue of my old Information Technology Newsletter. If you want solid information about ATAM and related approaches read Evaluating Software Architectures: Methods and Case Studies, which I reviewed on Amazon.
• IBM is another reliable source of information. I have long admired their objectivity, which I've witnessed firsthand in numerous consulting engagements where they have played a role (they have no problem recommending products that compete with what IBM sells, and will not hesitate to provide professional support for those products as well). In the web services domain they publish some of the best information that is available from a commercial vendor. One such document is Web Services Architecture Overview, which is entirely consistent with the W3C views cited above. I also like their PDF document titled Web Services Conceptual Architecture, which is packed with information and describes architecture in both abstract and practical terms. Introduction to Web Services Architecture is a more generic paper published by IBM, and is well illustrated (a picture is worth a thousand words in this case). Web Services and UDDI look beneath the architecture at some of the moving parts, and related whitepapers complete the picture.
• Web Services Architectures: How they stack up, also available as a PDF document, is an interesting comparison of different approaches to web services architectures.
• Yet another source of information (and viewpoint) is the O'Reilly Web Services FAQs, which address the technical underpinnings more than the architecture. Their book titled Web Services Essentials, and another book (published by Addison Wesley) titled XML, Web Services, and the Data Revolution are worth reading.
• Architecting Web Services by William L. Oellermann Jr. is a still valid early work that attempts to do the right thing: define an architecture that is traceable to business requirements. Although this book goes into technical details, it remains at a high enough level of abstraction to be a book about architecture. I especially like the book's web site, which provides a test environment that allows you to test your web services, and other resources. While this book is not strictly about architecture, it comes the closest to addressing web services architecture in the real world than any other I've read (or read about).
• Doug Kaye's Web Services Strategies weblog, which contains news, opinions and trends.

I've by no means exhausted my thoughts on this topic, and you can be sure that it will resurface again in the near future.

Bright Light. When Kate does return I promise that I'll make sure she stays around, and her place will never be filled until that time.