tailieunhanh - Báo cáo khoa học: "HANDLING LINEAR PRECEDENCE CONSTRAINTS BY UNIFICATION"

Linear precedence (LP) rules are widely used for stating word order principles. They have been adopted as constraints by HPSG but no encoding in the formalism has been provided. Since they only order siblings, they are not quite adequate, at least not for German. We propose a notion of LP constraints that applies to linguistically motivated branching domains such as head domains. We show a type-based encoding in an HPSG-style formalism that supports processing. The encoding can be achieved by a compilation step. . | HANDLING LINEAR PRECEDENCE CONSTRAINTS BY UNIFICATION Judith Engelkamp Gregor Erbach and Hans Uszkoreit Universitdt des Saarlandes Computational Linguistics and Deutsches Forschungszentrum fiir Kunstliche Intelligenz D-6600 Saarbriicken 11 Germany engelkamp@ ABSTRACT Linear precedence LP rules are widely used for stating word order principles. They have been adopted as constraints by HPSG but no encoding in the formalism has been provided. Since they only order siblings they are not quite adequate at least not for German. We propose a notion of LP constraints that applies to linguistically motivated branching domains such as head domains. We show a type-based encoding in an HPSG-style formalism that supports processing. The encoding can be achieved by a compilation step. INTRODUCTION Most contemporary grammar models employed in computational linguistics separate statements about dominance from those that determine linear precedence. The approaches for encoding linear precedence LP statements differ along several dimensions. Depending on the underlying grammatical theory different criteria are employed in formulating ordering statements. Ordering constraints may be expressed by referring to the category grammatical function discourse role and many other syntactic semantic morphological or phonological features. Depending on the grammar formalism different languages are used for stating the constraints on permissible linearizations. LP rules first proposed by Gazdar and Pullum 1982 for GPSG are used in different guises by several contemporary grammar formalisms. In Functional Unification Grammar Kay 1985 and implemented versions of Lexical Functional Grammar pattern languages with the power of regular expressions have been utilized. Depending on the grammar model LP statements apply within different ordering domains. In most frameworks such as GPSG and HPSG the ordering domains are local trees. Initial trees constitute the ordering domain in ID LP TAGS