A local approach to reasoning with conditional knowledge bases

The paper investigates a local approach for reasoning with conditional knowledge bases (with default rules of the form "generally, if /spl alpha/ then /spl beta/" and having possibly so,ne exceptions). The idea is that when a conflict appears (due to observing exceptional situations), one first localizes the sets of pieces of information which are responsible for conflicts. Next, using a specificity principle (subclasses must be preferred to general classes), the authors attach priorities to default rules inside each conflict. These priorities, implicitly computed from the knowledge base, reflect the hierarchical structure of the knowledge base. Lastly, they rank-order and solve conflicts in a way that only minimal sets of rules are given up from the knowledge base in order to restore its consistency. This local method of dealing with conflicts addresses correctly the well known problems of specificity, irrelevance, blocking of inheritance, etc.