Abstract
Keyword extraction is one of the technology essential for information retrieval. There are methods based on the statistical information of words and features in syntax of the documents as existing keyword extraction methods. Among these methods, there is a keyword extraction method based on only a statistics which is called adaptation without using the dictionary. This method has a problem that it is not possible to extract a keyword as a long character string when the number of documents is limited. In this research, we introduce an idea of repetition occurrence in two ormore documents based on the idea of query expansion. And, we propose a novel keyword extraction method based on this idea. The F measure of the proposed keyword extraction method is improved. And, it becomes possible to extract the keyword that was not able to be extract before. In conclusion, we report the usefulness of the document expansion in the keyword extraction.
