We describe the INEX 2004 participation of the Informatics Institute of the University of Amsterdam. We completely revamped our XML retrieval system, now implemented as a mixture language model on top of a standard search engine. To speed up structural reasoning, we indexed the collection's structure in a separate database. Our main findings are as follows. First, we show that blind feedback improves retrieval effectiveness, but increases overlap. Second, we see that removing overlap from the result set decreases retrieval effectiveness for all metrics except the XML cumulative gain measure. Third, we show that ignoring the structural constraints gives good results if measured in terms of mean average precision; the structural constraints are, however, useful for achieving high initial precision. Finally, we provide a detailed analysis of the characteristics of one of our runs. Based on this analysis we argue that a more explicit definition of the INEX retrieval tasks is needed.
['Börkur Sigurbjörnsson', 'Jaap Kamps', 'M. de Rijke']
Mixture models, overlap and structural hints in XML element retrieval