Literal Movement Grammars

Literal Movement Grammars Annius V. Groenink* CWI Kruislaan 413 1098 SJ Amsterdam The Netherlands avg@cwi,nl Abstract Literal movement grammars (LMGs) pro- vide a general account of extraposition phe- nomena through an attribute mechanism al- lowing top-down displacement of syntacti- cal information. LMGs provide a simple and efficient treatment of complex linguistic phenomena such as cross-serial dependen- cies in German and Dutch--separating the treatment of natural language into a parsing phase closely resembling traditional context- free treatment, and a disambiguation phase which can be carried out using matching, as opposed to full unification employed in most current grammar formalisms of linguistical relevance. 1 Introduction The motivation for the introduction of the literal move- ment grammars presented in this paper is twofold. The first motivation is to examine whether, and in which ways, the use of unification is essential to automated treatment of natural language. Unification is an ex- pensive operation, and pinpointing its precise role in NLP may give access to more efficient treatment of language than in most (Prolog-based) scientific appli- cations known today. The second motivation is the desire to apply popular computer-science paradigms, such as the theory of attribute grammars and modu- lar equational specification, to problems in linguistics. These formal specification techniques, far exceeding the popular Prolog in declarativity, may give new in- sight into the formal properties of natural language, and facilitate prototyping for large language applica- tions in the same way as they are currently being used to facilitate prototyping of programming language tools. For an extensive illustration of how formal specifi- cation techniques can be made useful in the treatment of natural language, see (Newton, 1993) which de- scribes the abstract specification of several accounts of phrase structure, features, movement, modularity and *This work is supported by SION grant 612-317-420 of the Netherlands Organization for Scientific Research ~wo). 90 parametrization so as to abstract away from the exact language being modelled. The specification language (ASL) used by Newton is a very powerful formalism. The class of specification formalisms we have in mind includes less complex, equational techniques such as ASF+SDF (Bergstra et al., 1989) (van Deursen, 1992) which can be applied in practice by very efficient exe- cution as a term rewriting system. Literal movement grammars are a straightforward extension of context-free grammars. The derivation trees of an LMG analysis can be easily transformed into trees belonging to a context-free backbone which gives way to treatment by formal specification systems. In order to obtain an efficient implementation, some restrictions on the general form of the formalism are necessary. 1.1 Structural Context Sensitivity in Natural Language Equational specification systems such as the ASF+SDF system operate through sets of equations over signatures that correspond to arbitrary forms of context-free grammar. An attempt at an equa- tional specification of a grammar based on context- free phrase structure rules augmented with feature con- straints may be to use the context-free backbone as a signature, and then implement further analysis through equations over this signature. This seems entirely ana- …

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