In this paper, we propose a syntax-based text retrieval system for on-line language learning and use a fast regular expression search engine as its main component. Regular expression searches provide more scalable querying and search results than keyword-based searches. However, without a well-designed index scheme, the execution time of regular expression search would be unacceptable to users. Our methods are based on Cho and Rajagopalan ( 2002) and we introduce some modifications, such as a presuf index constructing algorithm and a method for deciding minimum filter factor, to meet the requirements of our syntax-based text retrieval system. The experiment results show the index space size is small and the performance of syntax-based sample queries show significant improvements over benchmark results. A user-friendly query generator is designed to support users who have no background knowledge of regular expressions.
