Tools for rules

The dust was thick on my copy of the 1985 Clocksin and Mellish classic, Programming Prolog. But Ted Neward, author of the forthcoming book Effective Enterprise Java, brought it all rushing back: expert systems, declarative rules engines, predicate calculus, backward- vs. forward-chaining evaluation.

Neward gives an example on his weblog why this obscure discipline is back in vogue.

"If the guy filing the expense report files a 334-B form, then the upper limit on the total is twice his Personal Expense Liability total (which you get from the HR database, of course), unless his boss is an Assistant Vice President, in which case we have to get departmental approval from two managers and the AVP himself." [The Mountain of Worthless Information]

Today we program this stuff in procedural languages, and we make a hell of a mess doing so. Wouldn't it be great if we could declare a bunch of rules and have a rules engine work out the consequences? As Ted points out, this is the moral equivalent of using SQL to say what you want done with data not how. [Full story at]

For those (like me) who haven't followed recent developments in the world of rules engines, here are some signposts:

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