The Impact of Document Level Ranking on Focused Retrieval

Document retrieval techniques have proven to be competitive methods in the evaluation of focused retrieval. Although focused approaches such as XML element retrieval and passage retrieval allow for locating the relevant text within a document, using the larger context of the whole document often leads to superior document level ranking. In this paper we investigate the impact of using the document retrieval ranking in two collections used in the INEX 2008 Ad hoc and Book Tracks; the relatively short documents of the Wikipedia collection and the much longer books in the Book Track collection. We experiment with several methods of combining document and element retrieval approaches. Our findings are that 1) we can get the best of both worlds and improve upon both individual retrieval strategies by retaining the document ranking of the document retrieval approach and replacing the documents by the retrieved elements of the element retrieval approach, and 2) using document level ranking has a positive impact on focused retrieval in Wikipedia, but has more impact on the much longer books in the Book Track collection.