acm address algorithm american analysis approach association assume assumed assumption automatic average based binary called case class classes classification cluster clustering clusters collection computer conditions cut data decision defined dependence discrimination distribution distributions document documentation documents early effectiveness evaluation expected experimental fact figure file form found frequency function general good hypothesis importance important independence index indexing information jones journal key keyword keywords kind lambda language large length level line link list logical london made make matching means measure measurement measures method methods model node number objects order paper part performance phi point points precision probabilistic probability problem process processing propersubset queries query recall record records related relevance relevant report representation representative representatives request research results retrieval retrieved robertson rule salton science search set shown simple simply single sparck statistical storage stored strategies strategy structure structures system systems table techniques term terms test text theory time tree university user values ways weighting word words work york