Knowledge Refinement Through Revision

Refining a logical knowledge base by means of a more precise or detailed piece of information that takes the form of a weaker formula is a complex issue when deduction is used for inference and question-answering. Indeed, the direct insertion of a logically weaker formula inside a stronger base is not satisfactory since this formula is then subsumed and does not entail any actual new information from a logical point of view. In this respect, stronger -but sometimes less informative-knowledge can subsume and hide epistemologically more precise or detailed pieces of information. In order to allow one to refine a logical base by means of logically weaker knowledge, we introduce an approach that enforces the predominance of the new piece of information by expelling the already present subsuming knowledge. Interestingly enough, this approach appears to be a practical application for belief revision techniques.