Thursday, April 29, 2004

Declarative Application Building considered dangerous 

via Tim Bray

Declarative Application Building This is the idea, most publicly on display in the various flavors of BPEL and WS-Choreography, that you don’t need to write a bunch of icky procedural code to deploy your sophisticated Web-Services application. You write a bunch of declarative statements, which is good, only they’re in XML, which is better. Once you’ve written them, your application builds itself!

Sounds great, right? Except for I’ve seen this movie before; twice, in fact. The first time was during the Eighties with the advent of the 4GL’s (“Fourth-Generation Languages”), whose value proposition read more or less exactly the same: build your application declaratively and let us take care of the details. Then again in the Nineties, there was a (now mostly forgotten) class of application called “Workflow”; the idea was you diagrammed out your business processes as a sequence of events. You could put in conditional branches and loopback conditions, and there were these way-cool graphic front-ends so you could actually see the processes right there on the screen. Then the workflow applications would route your work among the fallible human cogs who actually did it, only there wouldn’t be expensive mistakes any more.

There were some problems, though. It turned out with 4GL’s, you could build 90% of your application in no time at all, but there always seemed to be one or two little pieces that were necessary but required some tricky procedural code and took endless effort to get done, and sometimes you couldn’t.

And as regards the workflow products, I never once heard of a single successful deployment of a complex automated-workflow scenario on any scale. It works OK for simple workflows, like at an HMO: so many thousand transactions come in the door every day, most get approved and paid, a smaller proportion get kicked up to second level, then human judgment takes over. But complex workflows resist automation, mightily.

Once again, I’m not saying it can’t be done, or that it’s not a good idea. I’m just saying that it’s not a safe bet today for the prudent businessperson.

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