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  2. RPG400-L
  3. December 2006

Re: Legacy question

In general though, if rules are hard-coded, the programmer has to
maintain them, while a table driven is maintained by the user.
Absolutely correct. And that's where you start your analysis. If it turns out that it's a case of the accounting department calling twice a week to have you add an entry to a compile-time table, by all means move that to a database file, change the LOOKUP to a CHAIN, build a maintenance program for it and turn your accounting department loose! That's a lot of benefit for a very small amount of work.
Pick off all the low-hanging fruit that way, and the bulk of your fiddly work is over, for a fairly small expenditure of effort. It's easy to make a program do one specific thing with a file. Writing a generic rules-processing engine is outside the experience base of almost all the programmers reading this note. That's not to disparage us, but to bring home just how unusual this job is.
Having worked for a software vendor, I have written what I would call a primitive rules processing engine and deployed it to production. I'm afraid I can't share that code for contractual reasons. Sketching out the code is easy, the database is a bit harder. Hands down, maintenance is the hardest part, and end users were never able to understand the rules database enough to implement new rules. I fault myself for this, not the end users. Changes to existing rules were OK, but I did not have an intuitive mechanism (wizard?) to create new rules from scratch.
There is no wrong answer and I'm not trying to discourage you. This has been my own real world experience; maybe there's value to others in sharing it. 
  --buck

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