Invalidity Search for USPTO Patent Documents Using Different Patent Surrogates

2. The Invalidity Search Task This paper describes our work at the sixth NTCIR workshop on the subtask of invalidity search for patent retrieval. We compared different patent surrogates for their effectiveness on invalidity search. Our preliminary results show that the query by the Claims field plus PRF (pseudo relevance feedback) leads to the best results in terms of relevance degree A while the query by all free-text fields yields highest performance under relevance degree B. Keywords: Probabilistic retrieval model, relevance feedback, effectiveness, patent surrogates. 1