Pictorial Relationships-a Syntactic Approach

Grammars or syntax specifications address themselves to the characterisation in symbolic terms of the structure of complex expressions. Two types of expression of empirical interest have been studied: sentences in English and other 'natural' languages, and programs written in some high-level procedural language like ALGOL. Expressions in these languages consist of sets of elements (words and characters) co-ordinated with one another according to the sensorily manifest relationship 'alongside', more commonly termed 'followed by'. (In the case of context-sensitive phrase-structure grammars it may also be 'on both sides of', more commonly termed 'bounded by' or 'in the context of'.) A grammar seeks to relate, by translation or mapping, this manifestation of the expression into another in which the same elements together with others (e.g. 'Noun Phrase', 'Simple arithmetic expression', etc.) are co-ordinated by abstract relationships which in the case of English and ALGOL is the . single relationship 'parts of'. The notation used to exhibit this relationship is some tree-structure representation in which elements are associated with (i.e., label) the nodes of the tree. A syntactically motivated parser is a device which accesses elements of the sensorily manifest expression, by application of an addressing procedure, e.g. 'Next char' which embodies their sensorily manifest relationship. The parser develops a representation in which elements are co-ordinated by the abstract relationship ('parts of'), through application of an addressing procedure, e.g. 'Ti' or 'Cdr' (Woodward 1966) which embodies this abstract relationship. In a free paraphrase of Chomsky we might say that a parser translates some set of surface relationships on elements, into some set of underlying relationships on those (and other) elements. Thus, according to Chomsky