The concept of NL-computation
NL-computation has a position of centrality in GTU. The basic structure of NL-computation, viewed as the core of PNL, is shown in Figure 6.3. The point of departure is a given proposition or, more generally, a system of propositions, p, which constitutes the initial information set described in a natural language (INL). In addition, what is given is a query, q, expressed in a natural language (QNL). The problem is to compute an answer to q given p, ans(qp). In GTU, deduction of ans(qp) involves these modules: (a) precisiation module, P; (b) protoform module, Pr; and (c) computation/deduction module, C/D. Informally, precisiation is an operation which precisiates its operand. The operand and the result of precisiation are referred to as "precisiand" and "precisiand", respectively. The precisiation module operates on the initial information set, p, expressed as INL, and results in a precisiand, p*. The protoform module serves as an interface between the precisiation module and the computa- tion/deduction module. The input to Pr is a precisiand, p*, and its output is a protoform of p*, that is, its abstracted summary, p**. The computa- tion/deduction module is basically a database (catalog) of deduction rules which for the most part are rules that govern generalized constraint propagation and counter-propagation. The principal deduction rule is the Extension Principle (Zadeh, 1965; 1975b). The rules are protoformal, with each rule having a symbolic part and a computational part. Protoformal rules are grouped into modules, with each module comprising rules which are associated with a particular class of generalized constraints, for example, possibilistic constraints, probabilistic constraints,
Figure 6.3 NL computation—basic structure (pNL)
Figure 6.4 Computational/deduction module
veristic constraints, usuality constraints, and so forth (see Figure 6.4). The inputs to the C/D module are p** and q**. A module which plays an important role in C/D is the world knowledge module (WK). World knowledge is the knowledge which humans acquire through experience, education, and communication (Zadeh, 2004a; 2004b). Much of the information in WK is perception-based. Organization of knowledge in WK is a complex issue which is not addressed in the present chapter.