Thomson Legal and Regulatory at NTCIR-3: Japanese, Chinese and English Retrieval Experiments

Thomson Legal and Regulatory participated in the CLIR task of the NTCIR-3 workshop. We submitted formal runs for monolingual retrieval in Japanese and Chinese, and for bilingual retrieval from English to Japanese. Our main focus was in Japanese retrieval. We compared word-based and character-based indexing, as well as query formulation using characters and character bigrams. Our results show that wordbased and bigram-based retrieval show similar performance for most query formulation approaches, while they outperform character-based retrieval. For Chinese retrieval, we compared using single characters with using character bigrams. We also introduced a structured query to leverage both. Our results are consistent with previous work, where character bigrams were shown to have better performance than single characters. The structured query approach is promising, but requires more analysis. In our bilingual runs, queries were translated using a machine-readable dictionary. Translated terms were resegmented to match indexing units. Our results, so far, are inconclusive, as we experienced unexpected query formulation issues especially in our word-based approach.