While I'm on the subject of rules engines (which seem to be my main blogging topic currently), I should report that during the last two or three weeks, I took the plunge and expanded (rather a lot) the Wikipedia article of the Rete algorithm. See http://en.wikipedia.org/wiki/Rete_algorithm. Originally, I used the text of an explanation I wrote a year or so ago. I got some kickback on that, with claims of inaccuracy and other claims that the text was too convoluted (what, me write convoluted content - impossible!). The original text wasn't inaccurate, but it was less comprehensive than it should have been, and lacking clarity in places. I spent some time last week extensively re-writing and expanding it, and have published the new version. I’m not sure it’s any easier to read, but it is more complete. Rete is a specialist subject, but if you are interested in how rules engines like MS BRE work internally, and specifically how they approach the problem of doing efficient combinatorial pattern-based matching of facts to rule conditions, then take a look. I've added in links to other Wikipedia articles, and I plan at some point to add a few more diagrams. Being Wikipedia, of course, anyone is free to alter, extend, re-write or even delete the content, so if you're also a Rete-head, please feel free.
Previously posted at http://blog.solidsoft.com/blogs/charles_young_mvp_biztalk/default.aspx