Trec 7 Ad Hoc, Speech, and Interactive Tracks at Mdsscsiro 2.1 System Description

In TREC-5 we used document retrieval based on arbitrary passages [8, 9], or xed-length passages that could start at any word position. Although far from the best runs in TREC5, these results were promising, in particular for long documents. In TREC-6 we continued with arbitrary passages, but our main emphasis was on comprehensive factor analysis of successful automatic query expansion and re nements methods in the context of the vector space model [5]. This year we have re ned the MG retrieval system to include Rocchio-based relevance feedback. Also, phrase matching has been added. We have continued to use arbitrary passages and combination of evidence for document retrieval.