The tolerance continuum

I distinctly remember the first time I heard the term AJAX. I was having dinner with a friend who mentioned, in passing, that he'd been interviewed on that topic. "AJAX?" I asked. "Asynchronous JavaScript and XML," he replied.

Whew. For a moment I thought I might have missed an important trend. But it turned out to be simply a new buzzword for an old set of technologies. No big deal, I figured. After all, what's in a name? Boy, was I wrong. Within a couple of weeks, you couldn't turn around without tripping over a new AJAX toolkit, or an AJAXified version of a Web application.

It's easy to be cynical about the fog of terminology that rises up from the technology landscape. But don't underestimate the power of a newly coined word, phrase, or acronym. AJAX -- the term, not the concepts behind it -- turned out to be an enzyme that catalyzed a powerful reaction. JavaScript, dynamic HTML, the document object model, and XML parsers had been there all along. It was our perception of them that suddenly made these ingredients crystallize into something shiny and new.

In that vein, here's another verbal enzyme that I hope will have a similar effect: the tolerance continuum. It's being used, in SOA circles, to break through the conceptual logjam we explored in our cover story back in September. How do you harness the advantages of REST (Representational State Transfer) and RSS, on the one hand, and XML Schema and WS-* on the other?

Tolerance, in this context, means broadly accessible services, open-ended data formats, and diverse communication protocols. The continuum ranges from our transactional mainframes, which can't and shouldn't allow much of this kind of tolerance, to our human touch points, which can and should.

It's hard to think about systems in this way. Consider security, for example. We imagine that we are either safe or not. The understanding that our systems are spread out along a continuum of risk (and expensive mitigation of that risk) does not come to us easily.

The same holds true for SOA's continuum of tolerance. But the meme seems to be spreading. I heard it first from Blue Titan's founder, Frank Martinez. Then I read InfoWorld contributing editor Phil Windley's list of criteria for evaluating the costs and benefits of tolerance. Windley in turn cited consultant/CTO Dion Hinchcliffe, who charted a continuum of technologies ranging from what I've called "WS-Lite" (accessible, simple, agile) to "WS-Heavy" (secure, reliable, stable). Hinchcliffe's blog in turn attributed the meme to another CTO/consultant, MomentumSI founder Jeff Schneider, who is, not coincidentally, an associate of Frank Martinez.

The trail doesn't end there. Schneider recalls a presentation by IBM distinguished engineer Kerrie Holley that captured the idea without using the exact phrase. And I even hear echoes of Internet pioneer Jon Postel: "Be liberal in what you accept, and conservative in what you send." That dictum remains a great organizing principle for a decentralized network.

Now that the nodes of that network run the gamut from personal communicators to corporate mainframes, we'll need a complementary metaphor to crystallize our thinking about these very unequal kinds of peers. What MindReef's Frank Grossman calls "WS-JustRight" isn't a point along the tolerance continuum, somewhere between WS-Heavy and WS-Lite. It is the continuum.

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Jon Udell

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