REINA at CLEF 2009 Robust-WSD Task: Partial Use of WSD Information for Retrieval

This paper describes the participation of the REINA research group at CLEF 2009 Robust-WSD Task. We have participated in both monolingual and bilingual subtasks. In past editions of the robust task our research group obtained very good results for non-WSD experiments applying local query expansion using co-occurrence based thesauri constructed using windows of terms. We applied it again. For WSD experiments, our intention was to use the WSD information and WordNet for expansion, but we did not have time to use them. We only used the lemma proposed by the POS tagger of the WSD collection as a stemmer. In bilingual retrieval experiments, two on-line machine translation programs were used to translate topics, and translations were merged before performing a monolingual retrieval. We also applied the same local expansion technique. Our non-WSD runs obtained the top rank considering the GMAP measure (monolingual and bilingual subtasks). However, regarding expansion we viewed that the settings tuned for a system not always produces retrieval improvement when the conditions change: number of query terms, query language, document or query subject, linguistic approach, etc. Our WSD runs also obtained very good positions in the rankings even thought we only used partial WSD information. However, in comparison with non-WSD runs the retrieval performance made worse. We detected some homonym errors in the POS tagger and probably these errors are worse than the errors carried out by the Porter stemmer used in the non-WSD experiments.