DCU at the NTCIR-12 SpokenQuery&Doc-2 Task

We describe DCU’s participation in the NTCIR-12 SpokenQuery&Doc (SQD-2) task. In the context of the slide-group retrieval sub-task, we experiment with a passage retrieval method that re-scores each passage according to the relevance score of the document from which the passage is taken. This is performed by linearly interpolating their relevance scores which are calculated using the Okapi BM25 model of probabilistic retrieval for passages and documents independently. In conjunction with this, we assess the benefits of using pseudo-relevance feedback for expanding the textual representation of the spoken queries with terms found in the top-ranked documents and passages, and experiment with a general multidimensional optimisation method to jointly tune the BM25 and query expansion parameters with queries and relevance data from the NTCIR-11 SQD-1 task. Retrieval experiments performed over the SQD-1 and SQD-2 queries confirm previous findings which affirm that integrating document information when ranking passages can lead to improved passage retrieval effectiveness. Furthermore, results indicate that no significant gains in retrieval effectiveness can be obtained by using query expansion in combination with our retrieval models over these two query sets.