Support Rulebase Inheritance

[dyoder]

We can imagine rulebases as classes with class methods that allow adding conditions, actions, and rules. These would update class variables: in effect, the class itself would take the place of the engine datastructure we currently use (or it could simply provide an alternative interface).

The advantage of this would be that we could quite naturally use inheritance to extend a rulebase. In fact, we could even use mixins. These could provide a shared “vocabulary” of conditions and actions from which to construct the rules.