Cancellation in a Parallel Semantic Network

Abstract

Handling exceptions to general rules is a persistent and difficult problem in systems for representing knowledge. In semantic networks, this often takes the form of cancelling some item of information, such as membership in a class, that would otherwise be inherited from a higher level description in the type hierarchy. Some conceptually clean approaches to cancellation lead to great inefficiency in accessing the information in the network, and can negate much of the speed advantage that would otherwise be possible in a parallel network system such as NETL. In this paper we explore some of the interactions between cancellation and parallelism in semantic networks, and we propose a cancellation scheme that appears to be workable for NETLIike systems. I.