Disambiguating Grammatically Ambiguous Sentences By Asking

Disambiguating Grammatically Ambiguous Sentences By Asking M-~saru Tomita Computer Science Department Carnegie-Mellon University Pittsburgh, PA 15213 Abstract The problem addressed in this paper is to disambiguate grammatically ambiguous input semences by asking the user. who need not be a computer specialist or a linguist, without showing any parse trees or phrase structure rules. Explanation List Comgarison (ELC) is the technique that implements this process. It is applicable to all parsers which are based on phrase structure grammar, regardless of the parser implementation. An experimental system has been implemented at Carnegie-Mellon University, and it has been applied to English-Japanese machine translation at Kyoto University. 1. Introduction /~ F=rge number of techniques using semantic information have been deve!oped to resolve natural language ambiguity. However, not all ambiguity problems can be solved by those techniques at the current state of art. Moreover, some sentences are absolutely ambiguous, that is, even a human cannot disambiguate them. Therefore. it is important for the system to be capable of asking a user questions interactively to disambiguate a sentence. Here, we make an important condition that an user is neither a computer scientist nor a linguist. Thus, an user may ROt recognize an;, spec=al terms or notations like a tree structure, phrase structure grammar, etc. The first system to disambiguate sentences by asking interactively is perhaps a program called "disambiguator" in Kay's MINO system [2]. Although the disambiguation algorithm is not presented in [2], some basic ideas have been already implemented in the Kay's system 2. In this paper, we shall only deal with grammatical ambiguity, or in other words, syntactic ambiguity. Other umhiguity problems, such as word-sense ambiguity and referential ambiguity, are excluded. Suppose a system is given the sentence: "Mary saw a man with a telescope" and the system has a phrase structure grammar including the following rules <a> - <g>: <a> S --> NP + VP <b> S --> NP + VP + PP <c> NP --> *noun <d> NP --> *det+ *noun <e> NP --> NP + PP <f> PP --> *prep + NP <g> VP --> *verb + NP The system would produce two parse trees from the input sentence (I. using rules <b>,<c>,<g>,<d>,<f>,<d>; II. using rules <a>,<c>,<g>,<e>,<d>,<f>,<d>). The difference is whether the preposition phrase "with a telescope" qualifies the noun phrase "a man" or the sentence "Mary saw a man". This paper shall discuss on how to ask the user" to select his intended interpretation without showing any kind of tree structures or phrase structure grammar rules. Our desired questior~ for that sentence is thus something like: 1) The action "Mary saw a man" takes place "with a telescope" 2) "a man" is "with a telescope" NUMBER ? The technique to implement this, which is described in the following sections, is called Explanation List Comparison. 2. Explanation List Comparison The basic idea is to attach an Explanation Template to each rule. For example, each of the rules <a> - <g> would have an explanation template as follows: <a> <b> <c> <d> …

Content truncated to 500 words