tailieunhanh - Báo cáo khoa học: "Guiding a Constraint Dependency Parser with Supertags"

We investigate the utility of supertag information for guiding an existing dependency parser of German. Using weighted constraints to integrate the additionally available information, the decision process of the parser is influenced by changing its preferences, without excluding alternative structural interpretations from being considered. The paper reports on a series of experiments using varying models of supertags that significantly increase the parsing accuracy. In addition, an upper bound on the accuracy that can be achieved with perfect supertags is estimated. . | Guiding a Constraint Dependency Parser with Supertags Kilian Foth Tomas By and Wolfgang Menzel Department fur Informatik Universitat Hamburg Germany foth by menzel@informatik .uni-hamburg . de Abstract We investigate the utility of supertag information for guiding an existing dependency parser of German. Using weighted constraints to integrate the additionally available information the decision process of the parser is influenced by changing its preferences without excluding alternative structural interpretations from being considered. The paper reports on a series of experiments using varying models of supertags that significantly increase the parsing accuracy. In addition an upper bound on the accuracy that can be achieved with perfect supertags is estimated. 1 Introduction Supertagging is based on the combination of two powerful and influential ideas of natural language processing On the one hand parsing is at least partially reduced to a decision on the optimal sequence of categories a problem for which efficient and easily trainable procedures exist. On the other hand supertagging exploits complex categories . tree fragments which much better reflect the mutual compatibility between neighbouring lexical items than say part-of-speech tags. Bangalore and Joshi 1999 derived the notion of supertag within the framework of Lexicalized Tree-Adjoining Grammars LTAG Schabes and Joshi 1991 . They considered supertagging a process of almost parsing since all that needs to be done after having a sufficiently reliable sequence of supertags available is to decide on their combination into a spanning tree for the complete sentence. Thus the approach lends itself easily to preprocessing sentences or filtering parsing results with the goal of guiding the parser or reducing its output ambiguity. Nasr and Rambow 2004 estimated that perfect supertag information already provides for a parsing accuracy of 98 if a correct supertag assignment were available. Unfortunately .