Information retrieval (IR) systems have tremendously broaden users' access to information. However, users need to select their needs from trillions of information indexed daily. Due to the "semantic gap" between queries and indexed terms in IR system, whether users can satisfy their needs depends on whether they use the correct terms as…

The tremendously huge volume of biomedical literature, scientists' specific information needs, long terms of multiples words, and fundamental problems of synonym and polysemy have been challenging issues facing the biomedical information retrieval community researchers. Search engines have significantly improved the efficiency and effectiveness of…

Search engines have now become essential tools in all aspects of our life. Although a variety of information needs can be served very successfully, there are still a lot of queries that search engines can not answer very effectively and these queries always make users feel frustrated. Since it is quite often that users encounter such "difficult…