Fusion of Probabilistic Algorithms for the CLEF Domain Specific Task

1 Extended Abstract This extended abstract describes the Berkeley 1 participation in the Domain Specific task for CLEF 2005. This year we submitted the minumum number of entries for each subtask (3 monolingual runs, 6 bilingual runs, and 3 multilingual runs). In our runs we employed retrieval algorithms data fusion methods that have performed relatively well in some other retrieval contexts, but which will almost surely be abandoned in later attempts at CLEF. The main technique being tested is the fusion of multiple probabilistic searches against different XML components using both Logistic Regression (LR) algorithms and a version of the Okapi BM-25 algorithm. We also combine multiple translations of queries in cross-language searching. In the following paragraphs we will briefly describe the the indexing and term extraction methods used, followed by a description of the retrieval algorithms and data fusion methods. Since this is the first time that the Cheshire system has been used for CLEF, this approach can at best be considered a very preliminary base testing of some retrieval algorithms and approaches. For both the monolingual and bilingual tasks we indexed the documents using the Cheshire II system. The document index entries and queries were stemmed using the Snowball stemmer. Text indexes were created for separate XML elements (such as document titles or dates) as well as for the entire document. The techniques and algorithms used for the DS task were essentially identical to those that we used for the GeoCLEF task, but without the special geographic indexes used for GeoCLEF (our GeoCLEF track paper describes the algorithms and approaches in detail). For the bilingual and multilingual search tasks we used combinations of up to three different MT systems for query translation, using the L&H PC-based system, SYSTRAN (via Babelfish), and PROMT. Each of these translations was combined into a single probabilistic query. The hope was to overcome the translation errors of a single system by including alternatives. However, for translation to Russian from German and English, only the PROMT MT system was available.