SNe PS - SNePS As A Logic-Based System

SNePS As A Logic-Based System

As a logic-based system, a SNePS KB consists of a set of terms, and functions and formulas over those terms. The set of logical connectives and quantifiers extends the usual set used by first-order logics, all taking one or more arbitrarily-sized sets of arguments. In accord with the intended use of SNePS to represent the mind of a natural-language-competent intelligent agent, propositions are first-class entities of the intended domain, so formulas are actually proposition-denoting functional terms. SNePSLOG, the input-output language of the logic-based face of SNePS, looks like a naive logic in that function symbols (including "predicates"), and formulas (actually proposition-denoting terms) may be the arguments of functions and may be quantified over. The underlying SNePS, however, is a first order logic, with the user's function symbols and formulas reified.

Formula-based inference is implemented as a natural-deduction-style inference engine in which there are introduction and elimination rules for the connectives and quantifiers. SNePS formula-based inference is sound but not complete, as rules of inference that are less useful for natural language understanding and commonsense reasoning have not been implemented.

A proposition-denoting term in a SNePS KB might or might not be "asserted", that is, treated as true in the KB. The SNePS logic is a paraconsistent version of relevance logic, so that a contradiction does not imply anything whatsoever. Nevertheless, SNeBR, the SNePS Belief Revision subsystem, will notice any explicit contradiction and engage the user in a dialogue to repair it. SNeBR is an Assumption-Based Truth Maintenance System (ATMS), and removes the assertion status of any proposition whose support has been removed.