ABSTRACT
The notation for representing phrase structure rules introduced in the last chapter is not ideally suited for treating some important aspects of the grammars of natural languages such as English. However, it can be extended in two simple ways by (i) treating grammar symbols as complex terms and (ii) allowing the inclusion of procedure calls into the body of the rule. Since the grammar formalism is expressed as a series of Prolog facts and rules and since such expressions are sometimes referred to as ‘definite clauses’, grammars of this sort are known as definite clause grammars (DCGs). The result is a powerful and flexible grammar formalism, well-suited to describing a wide range of syntactic constructions. The hope is that the reader will be inspired to use the various techniques described in this chapter to write grammar fragments for areas of English syntax not covered in this chapter as well as applying them to languages other than English.
