Access to Legal Documents: Exact Match, Best Match, and Combinations

In this paper, we document our efforts in participating to the TREC 2007 Legal track. We had multiple aims: First, to experiment with using different query formulations, trying to exploit the verbose topic statements. Second, to analyse how ranked retrieval methods can be fruitfully combined with traditional Boolean queries. Our main findings can be summarized as follows: First, we got mixed results trying to combine the original search request with terms extracted from the verbose topic statement. Second, by combining the Boolean reference run wit our ranked retrieval run allows us to get the high recall of the Boolean retrieval, whilst precision scores show an improvement over both the Boolean and the ranked retrieval runs. Third, we found out that if we treat the Boolean query as free text with varying degrees of interpretation of the original operator, we get competitive results. Moreover, both types of queries seem to capture different relevant documents, and the combination between the request text and the Boolean query leads to substantial gain in precision and recall.