Overview of the NTCIR-5 WEB Query Term Expansion Subtask

The query term expansion subtask was conducted to establish an evaluation framework for information retrieval (IR) systems that focus on the effectiveness of query term expansion techniques. However, the quality of query term expansions are affected by several factors (e.g., IR system using expanded query, quality of initial query, etc.), so it is difficult to evaluate this technique. In this subtask, I assume the topic difficulty for the query term expansion technique is caused by the mismatch between different information-need expressions (query terms and relevant documents). To take into account this topic difficulty, I propose feature quantities to characterize this difficulty and propose a new framework to evaluate each query expansion system.