Assessing the Impact of Thesaurus-Based Expansion Techniques in QA-Centric IR

In this paper, we assess the impact of using thesaurus-based query expansion methods, at the Information Retrieval (IR) stage of a Question Answering (QA) system. We focus on expanding queries for questions regarding actions and events, where verbs have particularly important roles. Two different thesaurus are used: the OpenOffice thesaurus and an automatically generated verb thesaurus. The performance of thesaurus-based methods is compared against what is obtained by (i) executing no expansion and (ii) applying a simple query generalization method. Results show that using thesaurus-based approaches helps to improve retrieval recall, while keeping satisfactory precision. However, we confirm that positive impact for the final QA performance is mostly achieved due to increase in recall, which can also obtained by alternative and simpler methods. Nevertheless, thesaurus-based expansion helps controlling the number of text passages retrieved, thus selectively reducing the computational load in the answer extraction stage.