Đang chuẩn bị nút TẢI XUỐNG, xin hãy chờ
Tải xuống
The f o r m a l i s m consists o f two parts: 1. A declarative description phrase-structures and t h e i r translation. of basic associated additional syntactic semantic grammar. PSGs have efficient algorithms for parsing [3]. In a sense, all o f the work of transformations has been pushed off into a p r e - p r o c e s s i n g phase w h e r e new g r a m m a r rules are d e r i v e d . | CAPTURING LINGUISTIC GENERALIZATIONS WITH METARULES IN AN ANNOTATED PHRASE-STRUCTURE GRAMMAR Kurt Konolige SRI International 1 Introduction Computational models employed by current natural language understanding systems rely on phrase-structure representations of syntax. Whether implemented as augmented transition nets BNF grammars annotated phrase-structure grammars or similar methods a phrase-structure representation makes the parsing problem computationally tractable 7 . However phrase-structure representations have been open to the criticism that they do not capture linguistic generalizations that are easily expressed in transformational grammars. This paper describes a formalism for specifying syntactic and semantic generalizations across the rules of a phrase-structure grammar PSG . The formalism consists of two parts 1. A declarative description of basic syntactic phrase-structures and their associated semantic translation. 2. A set of metarules for deriving additional grammar rules from the basic set. Since metarules operate on grammar rules rather than phrase markers the transformational effect of metarules can be pre-computed before the grammar is used to analyze input. The computational efficiency of a phrase-structure grammar is thus preserved. Metarule formulations for PSGs have recently received increased attention in the linguistics literature especially in 4 which greatly influenced the formalism presented in this paper. Our formalism differs significantly from 4 in that the metarules work on a phrase-structure grammar annotated with arbitrary feature sets Annotated Phrase-structure Grammar or APSG 71 . Grammars for a large subset of English have been written using this formalism 91 and its computational viability has been demonstrated 6 . Because of the increased structural complexity of APSGs over PSGs without annotations new techniques for applying metarules to these structures are developed in this paper and the notion of a match between a .
