Vo Ngoc Anh Raymond Wan Alistair Moffat Term Impacts as Normalized Term Frequencies for BM25 Similarity Scoring. 51-62 2008 SPIRE http://dx.doi.org/10.1007/978-3-540-89097-3_7 conf/spire/2008 db/conf/spire/spire2008.html#AnhWM08