12 - Head Corner Parsing

Abstract

This chapter describes a head-driven parser for a class of grammars that handle discontinuous constituency by a richer notion of string combination than ordinary concatenation. The parser is a generalization of the left-corner parser and can be used for grammars written in powerful formalisms, such as nonconcatenative versions of UCG and HPSG. In modern linguistic theories, much information is defined in lexical entries, whereas rules are reduced to very general (and very uninformative) schemata. More information usually implies less search space; hence, it is sensible to parse bottom-up to obtain useful information as soon as possible. Furthermore, in many linguistic theories a special daughter called the head determines what kind of other daughters there may be. Therefore, it is also sensible to start with the head to know what else one has to look for next. As the parser proceeds from head to head, it is furthermore possible to use powerful top-down predictions based on the usual head feature percolations. Subsequently, the parser may enter an infinite loop. However, in case the parser terminate, one can be sure that it has found all solutions. Moreover, the parser is quite efficient if the notion syntactic head implies that much syntactic information is shared between the head of a phrase and its mother.