why do successful search systems fail for some topics
This paper describes and evaluates the vector-space and probabilistic IR models used to retrieve news articles from a corpus written in the French language. Based on three CLEF test-collections and 151 queries, we classify the poor retrieval results of difficult topics under 6 categories. The explanations we obtain from this analysis differ from those suggested a priori by our students. We use the Web to manually or automatically find related search terms to the original query. We evaluate these two query expansion strategies in order to improve mean average precision (MAP) and to reduce the number of topics for which no pertinent responses are listed among the top ten references returned.
failure analysis robust evaluation