http://reply.papertrans.cn/2/101/10082/10082-31.png
http://reply.papertrans.cn/2/101/10082/10082-32.png
http://reply.papertrans.cn/2/101/10082/10082-33.png
http://reply.papertrans.cn/2/101/10082/10082-34.png
Submitted on: 25 January 2005.
Revised on: 25 April 2005.
Accepted on: 27 May 2005.
___________________Foundations and Trends in Information Retrieval
http://reply.papertrans.cn/2/101/10082/10082-36.png