Cross-lingual Information Retrieval based on Multiple Indexes

In this paper we present the technical details of the retrieval system with which we participated at the CLEF09 Ad-hoc TEL task. We present a retrieval approach based on multiple indexes for different languages which is combined with a conceptbased retrieval approach based on Explicit Semantic Analysis. In order to create the language-specific indices for each language, a language detection approach is applied as preprocessing step. We combine the different indices through rank aggregation and present our experimental results with different rank aggregation strategies. Our results show that the use of multiple indices (one for each language) does not improve upon a baseline index containing documents in all languages. The combination with concept based retrieval, however, results in better retrieval performance in some of the cases considered. For the bi-lingual tasks the final retrieval results of our system were the 5th best results on the BL dataset and the second best on the BNF dataset.