Towards a Syntactic Account of Punctuation

Little notice has been taken of punctuation in the field of natural language processing, chiefly due to the lack of any coherent theory on which to base implementations. Some work has been carried out concerning punctuation and parsing, but much of it seems to have been rather ad-hoc and performance-motivated. This paper describes the first step towards the construction of a theoretically-motivated account of punctuation. Parsed corpora are processed to extract punctuation patterns, which are then checked and generalised to a small set of General Punctuation Rules. Their usage is discussed, and suggestions are made for possible methods of including punctuation information in grammars. 1 Introduction Ititherto, the field of punctuation has been almost completely ignored within Natural Language Processing, with perhaps the single exception of the sentence-final full-stop (period). The reason for this non-treatment has been the lack of any coherent theory Of punctuation on which a computational treatment could be based. As a result, most contemporary systems simply strip out punctuation in input text, and do not put any marks into generated texts. Intuitively, this s~ems very wrong, since punctuation is such an integral part of many written languages. If text in the real world (a newspaper, for example) were to appear without any punctuation marks, it would appear very stilted, ambiguous or infantile. Therefore it is likely that any computational system that ignores these extra textual cues will suffer a degradation in performance , or at the very least a great restriction in the class of linguistic data it is able to process. Several studies have already shown the potential for using punctuation within NLP. Dale (1991) has shown the positive benefits of using punctuation ill the fields of discourse structure and semantics, suggesting that it can be used to indicate degrees of rhetorical balance and aggre-gation between juxtaposed elements, and also that in certain cases a punctuation mark can determine the rhetorical relations that hold between two elements. In the field of syntax Jones (1994) has shown, through a comparison of the performance of a grammar that uses punctuation and one which does not, that for the more complex sentences of real language, parsing with a punctuated grammar yields around two orders of magnitude fewer parses than parsing with an nnpunctuated grammar, and that additionally the punctuated parses better reflect the linguistic structure of the sentences. Briscoe and Carroll (1995) extend this work to show the …