Re: Rules in a database

A bit of algebra first: any expression formed of atomic expressions, AND, OR and parentheses can be reduced to a "canonical" form, by using the De Morgan laws: a AND ( b OR c ) is equiv. to a AND b OR a AND c So a rule can eventually be reduced to "AND" groups, joined by "OR": a(1) AND... AND a(n) OR ... OR z(1) AND ... AND z(p) Each "AND" group contains 1 or more rules. Therefore, to model "input" rules: - store atomic rules in a table - store "AND" rule groups in a table (1-n relation to the "atomic" table) - store full rules in a table (1-n relation to the "AND" table) Now you can model "output" rules likewise, and finally create a table of associations between "input" and "output" rules Problem is: once you've flattened your rules to the canonical form, they can become illegible. So perhaps a hierarchical data model (XML) would be more appropriate, for your rules would remain human-legible (and thererfore human-maintainable) HTH Ignatius _________________________ ----- Original Message ----- From: "John" <ioannes@btinternet.com> To: <php-db@lists.php.net> Sent: Friday, February 06, 2004 15:35 Subject: [PHP-DB] Rules in a database > I work in tax and thus have to read legislation - some complex - and I > wanted to store some of the logic in a database so that if I know certain > conditions were true I could look up what results this might have. > > Thus I am thinking of having two tables - one of phrases and the other of > how these phrases are linked together as rules. A rule structure could be: > > IF A THEN B > IF A OR A1 OR A2 THEN B > IF A THEN B AND C > > I was wondering how to do this. For instance, each rule could be one record > in the table. The rules table has fields, IF and THEN. The ID field is the > rule ID. Assume the phrases are numbered. One IF record could say: > +/12/41/31/+/90/ meaning if phrases 12, 41 or 31 are true and phrase 90 is > true. Then if I have a real situation where condition 12 is true, for > instance, I can find it and access it using sub string functions. Does this > scheme seem OK? Has anyone done anything like this before? > > Regards, > > John > > -- > PHP Database Mailing List (http://www.php.net/) > To unsubscribe, visit: http://www.php.net/unsub.php > >