The IT Strategy Letter
March 10, 2003 (Subscribe)


Web Services Strategies
Web Hosting Strategies
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Web Services Strategies

Loosely Coupled: Sync Versus Async

Asynchronous interaction is a key component of loosely coupled systems. Here's an example I've found helpful to explain its implications:

Synchronous Interaction

To illustrate the differences between the synchronous and asynchronous styles of interaction, let's use the analogy of holiday gift shopping. Here's the situation: You have a list of three people for whom you want to purchase gifts, and you've got two choices. You can head for the shopping mall, or you can shop online. For the sake of the analogy, think of yourself (the buyer) and the clerk or online store (the merchant) as a pair of distributed systems. The figure below illustrates the interaction of these systems when you shop at the mall.

The shopping-mall model is synchronous because it's composed of a series of predictable steps that cannot be re-ordered. Specifically, you and the sales clerks alternate roles: You select a gift, a clerk sells it to you, and you repeat the process for the remaining gifts. Your actions are synchronized with those of the clerks, and you won't move on to the next clerk before completing the exchange with the current one.

Asynchronous Interaction

Next, let's examine the interaction between the two systems when you shop online, as illustrated below.

This is an example of the asynchronous interaction model, which differs from the synchronous model in two ways. First, the three ordering actions are predictable, but the three shipping actions are not. The shipments are initiated at seemingly random times and out of sequence, take different lengths of time, and arrive in yet another unpredictable sequence. Second, in the asynchronous model you can place all three orders, one immediately after another. The merchants send email acknowledgements in response to your orders, but you don't need to wait for one order to be acknowledged before placing the next. In other words, the buyer and merchant are no longer synchronized.

[Excerpted from Loosely Coupled--The Missing Pieces of Web Services.]
Posted Sunday, March 09, 2003 12:42:58 AM

Web-Services Security. In this excellent article on MSDN, David Chappell explains the basics of the current round of security-protocol proposals: WS-Security, WS-SecurityPolicy, WS-Trust, WS-SecureConversation, and the Web Services Security Profile for XML-Based Tokens. The content of David's article is mostly conceptual, and only mildly technical. [Source: CapeScience]
Posted Sunday, March 09, 2003 9:04:40 AM 

Ten Emerging Best Practices For Building SOAs. In the February 25 issue of ZapFlash, Jason Bloomberg gives his recommendations " to leverage the power and flexibility of Web Services strategically across the enterprise." One of my favorites:

The enterprise application story of the 1990s was all about suites. Buying a few large packages with several tightly integrated modules made more sense than going with a best-of-breed, "mix and match" approach, so the argument went, because integrating products from multiple vendors was such a nightmare. Web Services and SOAs reverse this argument, because Web Services can reduce the cost of integration to the point that best-of-breed approaches make solid economic sense.

And another of which Jason was the earliest champion:

One of the holy grails of software development is code reuse. In an SOA, developers should construct the Services to be as simple as possible, where they continually refactor them so that they are as broadly applicable as is practical. The resulting services are then reusable at runtime-nuggets of software functionality (both fine- and coarse-grained) that can be used in a variety of situations, as contrasted to typical code reuse, which is a design time principle.
Posted Thursday, March 06, 2003 2:17:27 PM

Don Box: Too Many Specs. The co-inventor of SOAP (now a Microsoft engineer) had harsh words last week for vendors contributing to the plethora of web-services specifications, and advised developers to read less of them and get on with writing applications.

Also from the XML Web Services One conference, Anne Thomas Manes, now with the Burton Group, said that upcoming specifications like WS-Security, being hammered out by Microsoft, IBM and Verisign Inc., will be useful for some, but in the meantime the existing SSL (Secure Sockets Layer) security standard "solves 80 percent" of security needs for Web services. [Source:]
Posted Thursday, March 06, 2003 10:42:19 AM

Web-Services Benefits. Thanks to Phil Windley for linking to this article by Lawrence Wilkes of the CBDi Forum (free registration required). Make sure you read the comments/discussion that follow Lawrence's article and Phil's own thoughts published in his weblog.
Posted Wednesday, March 05, 2003 2:07:59 PM

Web-Services Startups More than 100 web services startups are profiled in a new report compiled by Deloitte & Touche Corporate Finance. This is the most thorough coverage I've seen of early-stage companies in this niche. Thanks to an arrangement between D&T and Phil Wainewright, you can download the printable PDF through Phil's web site,
Posted Wednesday, March 05, 2003 7:53:27 AM

Web Hosting Strategies

AOL Caching Info I was repairing some broken links on my hosting resource page and I came across the updated information on caching in the AOL network.
Posted Sunday, March 09, 2003 10:12:37 AM

PC Magazine Looks at Hosting. It's always noteworthy when a mainstream/consumer magazine looks at a niche like web hosting. PC Mag compared seven of the largest companies for shared-server hosting: DellHost, EarthLink, Interland, NetNation, NTT/Verio, ValueWeb, and Yahoo! Obviously, they couldn't include the thousands of resellers in their review, but at leased the article explains:

But don't overlook smaller Web hosting companies. A blossoming market for hosting resellers has made it possible for companies to provide services targeted at underserved niches and specialized markets such as religious-themed sites. If you like the idea of actually talking to someone at the hosting company, your local ISP can't be beat for the personal touch.

Unfortunately, the article neither explained that most resellers use the facilities of the larger players nor how to go about locating and evaluating such a reseller.
Posted Sunday, March 09, 2003 9:34:44 AM

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"...essential reading for anyone seeking to deploy this technology."

--John Hagel, III,
management consultant
and author of
"Out of the Box"


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