Knowledge hierarchy

Should different ways of representing concepts and different types of deduction system be used on different levels of a knowledge hierarchy? Certainly physics and biology use different sorts of representation and different practices. In a few of my experiments with Asa H I have employed multiple different similarity measures. When forgetting is used to prune less useful cases/concepts I sometimes find one similarity measure dominates on one level of the abstraction hierarchy while a different similarity measure dominates on another level. (By dominates I mean gives results having the highest utility measures.)