Combination methods for crosslingual web retrieval

Abstract. We investigate a range of crosslingual web retrieval tasks using the test suite of the CLEF 2005 WebCLEF track, which features a stream of known-item topics in various languages. Our main findings are: (i) straightforward indexing and retrieval is effective for mixed monolingual web retrieval; (ii) standard machine translation methods are effective for bilingual web retrieval; but (iii) standard combination methods are ineffective for multilingual web retrieval; we analyze the failure and suggest an alternative Z-score normalization that leads to effective multilingual retrieval results.