Evaluating Parsing Schemes with Entropy Indicators

This paper introduces an objective metric for evaluating a parsing scheme It is based on Shannon s original work with letter sequences which can be extended to part of speech tag sequences It is shown that this regular language is an inadequate model for natural language but a representation is used that models language slightly higher in the Chomsky hierarchy We show how the entropy of parsed and unparsed sentences can be measured If the entropy of the parsed sentence is lower this indicates that some of the structure of the language has been captured We apply this entropy indicator to support one particular parsing scheme that e ects a top down segmentation This approach could be used to decompose the parsing task into computationally more tractable subtasks It also lends itself to the extraction of predicate argument structure