Holger Kache Wook-Shin Han Volker Markl Vijayshankar Raman Stephan Ewen POP/FED: Progressive Query Optimization for Federated Queries in DB2. 1175-1178 2006 conf/vldb/2006 VLDB http://www.vldb.org/conf/2006/p1175-kache.pdf db/conf/vldb/vldb2006.html#KacheHMRE06