Web Services Strategies
Beyond the technology, IT strategies for implementation of Web services by Doug Kaye.
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IT Conversation with John McDowall, CTO of Grand Central Communications. It's the audio version of John's top-ten list of Rules of Service Design:
- Design services to be shared.
- Services have a clear purpose.
- Services are discoverable and support introspection.
- Services plug into a SOA.
- Services can be loosely orchestrated and use other services whenever possible for common tasks.
- A service has a well-defined use policy/contract.
- Services accept well-defined input and deliver well-defined output.
- Services do not have hidden side effects (play well with others).
- Services are interfaces to or from processes.
- Services must provide visibility and an SLA.
[stream—download—discuss, 5.1 mb, 22 minutes, recorded 7/30/03]
Posted Thursday, August 14, 2003 10:59:29 PM 
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Gartner on Event-Driven Architectures. This is an excellent web seminar by Yefin Natis and Roy Schulte of Gartner in which they explain the concepts of asynchronous event-driven services. In his review of the presentation, Edwin Khodabakchian at Collaxa pointed out that the Gartner distinction between SOA and EDA may not be correct. Indeed, Gartner seems to have decided that the phrase "service-oriented architecture" can only apply to the request/response RPC-style synchronous MEP (message-exchange pattern). Most experts consider all MEPs, whether sync or async, to be under the SOA umbrella. But it's a detail, and the presentation is valuable nonetheless.
The total presentation runs an hour, but if you don't need the introduction to the basics of SOAs, skip to 27:00 and just listen to Schulte's half. (Make sure you get the right presentation. There may be more than one on the page.) That's where the event-driven elements are presented. I particularly liked Schulte's point that while synchronous systems involve a single reqeustor and responder, an event-driven asynch system publishes events which have a potentially unlimited number of subscribers (as in JMS). As he says, the flow is determined by the recipient, not the originator.
Posted Thursday, August 14, 2003 7:16:06 PM
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MSDN TV: Loosely Coupled Web Services Software legend-to-be Doug Purdy explains how to create .NET web services that are version resilient using the Open Content Model. Specifically, Doug shows how to write clients that can handle unknown versions (backward-compatible) without the need to recompile. It's a real-world example of loose coupling. [32mb WMV file]
Update: Radovan Janecek, VP engineering at Systinet, has a new blog that will focus on web services. (Welcome, Radovan!) He he points out that the technique Purdy demonstrates to obtain version resiliency depends on dumping structured data into an unstructured and untyped string. He's right: it's a bit of a quick-and-dirty gimmick. Still, I like the video because it demonstrates the problem if not the most elegant solution.
Posted Thursday, August 14, 2003 1:11:32 PM
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