THUIR at TREC 2003: Novelty, Robust and Web *

This is the second time that Tsinghua University Information Retrieval Group (THUIR) participates in TREC. In this year, we took part in four tracks: novelty, robust, web and HARD, describing in following sections, respectively. A new IR system named TMiner has been built on which all experiments have been performed. In the system, Primary Feature Model (PFM) has been proposed and combined with BM2500 term weighting , which led to encouraging results. Word-pair searching has also been performed and improves system precision. Both approaches are described in robust experiments (section 2), and they were also used in web track experiments.