Empirical Term Weighting.
Kyoji Umemura, Yoshiyuki Takeda, Michiko Tanaka, Feng Li, Eiko Yamamoto · 2001
Our system used an empirical method for estimating term weights directly from relevance judgements, avoiding various standard but potentially troublesome assumptions. It is common to assume, for example, that weights vary with term frequency ( ¢ ¡ ) and inverse