Kamesh Munagala Shivnath Babu Rajeev Motwani Jennifer Widom The Pipelined Set Cover Problem. 83-98 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3363&spage=83 2005 conf/icdt/2005 ICDT db/conf/icdt/icdt2005.html#MunagalaBMW05