tailieunhanh - Báo cáo khoa học: "DATR Theories and DATR Models"

Evans and Gazdar (Evans and Gazdar, 1989a; Evans and Gazdar, 1989b) introduced DATR as a simple, non-monotonic language for representing natural language lexicons. Although a number of implementations of DATR exist, the full language has until now lacked an explicit, declarative semantics. This paper rectifies the situation by providing a mathematical semantics for DATR. We present a view of DATR as a language for defining certain kinds of partial functions by cases. The formal model provides a transparent treatment of DATR's notion of global context | DATR Theories and DATR Models Bin Keller School of Cognitive and Computing Sciences The University of Sussex Brighton UK email billk@ Abstract Evans and Gazdar Evans and Gazdar 1989a Evans and Gazdar 1989b introduced DATR as a simple non-monotonic language for representing natural language lexicons. Although a number of implementations of DATR exist the full language has until now lacked an explicit declarative semantics. This paper rectifies the situation by providing a mathematical semantics for DATR. We present a view of DATR as a language for defining certain kinds of partial functions by cases. The formal model provides a transparent treatment of DATR s notion of global context. It is shown that DATR s default mechanism can be accounted for by interpreting value descriptors as families of values indexed by paths. 1 Introduction DATR was introduced by Evans and Gazdar 1989a 1989b as a simple declarative language for representing lexical knowledge in terms of path value equations. The language lacks many of the constructs found in general purpose knowledge representation formalisms yet it has sufficient expressive power to capture concisely the structure of lexical information at a variety of levels of linguistic description. At the present time DATR is probably the most widely-used formalism for representing natural language lexicons in the natural language processing NLP community. There are around a dozen different implementations of the language and large DATR lexicons have been constructed for use in a variety of applications Cahill and Evans 1990 Andry et al. 1992 Cahill 1994 . DATR has been applied to problems in inflectional and derivational morphology Gazdar 1992 Kilbury 1992 Corbett and Fraser 1993 lexical semantics Kilgariff 1993 morphonology Cahill 1993 prosody Gibbon and Bleiching 1991 and speech Andry et al. 1992 . In more recent work the language has been used to provide a concise encoding of Lexicalised Tree Adjoining Grammar Evans