In current keyword-based XML fragment retrieval systems, various granules of XML fragments are returned as retrieval results. The number of the XML fragments is huge, so this adversely affects the index construction time and query processing time of the XML fragment retrieval systems if they cannot extract only the answer XML fragments with certainty. In this paper, we propose a method for determining XML fragments that are appropriate in keyword-based XML fragment retrieval. This would help to improve overall performance of XML fragment retrieval systems. The proposed method utilizes and analyzes statistical information of XML fragments based on a technique of the dynamics of terminology in quantitative linguistics. Moreover, our keyword-based XML fragment retrieval system runs on a relational database system. In this paper, we briefly explain the implementation of our system.