CLEF-2005 CL-SR at Maryland: Document and query expansion using side collections and thesauri

This paper reports results for the University of Maryland's participation in the CLEF-2005 Cross-Language Speech Retrieval track. Techniques that were tried include: (1) document expansion with manually created metadata (thesaurus keywords and segment summaries) from a large side collection, (2) query refinement with pseudo-relevance feedback, (3) keyword expansion with thesaurus synonyms, and (4) cross-language speech retrieval using translation knowledge obtained from the statistics of a large parallel corpus. The results show that document expansion and query expansion using blind relevance feedback were effective, although optimal parameter choices differed somewhat between the training and evaluation sets. Document expansion in which manually assigned keywords were augmented with thesaurus synonyms yielded marginal gains on the training set, but no improvement on the evaluation set. Cross-language retrieval with French queries yielded 79% of monolingual mean average precision when searching manually assigned metadata despite a substantial domain mismatch between the parallel corpus and the retrieval task. Detailed failure analysis indicates that speech recognition errors for named entities were an important factor that substantially degraded retrieval effectiveness.