Ronan Cummins and Colm O'Riordan. Evolving local and global weighting schemes in information retrieval. Information Retrieval, 9(3):311-330, June 2006. (pdf) Also available from publisher’s site here

Ronan Cummins and Colm O'Riordan
. An analysis of the solution space for genetically programmed Term-Weighting schemes in Information Retrieval. In: P. M. D. Bell and P. Sage (eds.): 17th Artificial Intelligence and Cognitive Science Conference (AICS 2006). Queen's University, Belfast, Northern Ireland, September 2006. (pdf)

Ronan Cummins and Colm O'Riordan . Term-weighting in information retrieval using genetic programming: A three stage process. In The 17th European Conference on Artificial Intelligence, ECAI-2006, Riva del Garda, Italy, August 28th - September 1st 2006. (pdf)