Feng Zhao Xiaolong Zhang Anthony K. H. Tung Gang Chen 0001 BROAD: Diversified Keyword Search in Databases. 1355-1358 2011 4 PVLDB 12 http://www.vldb.org/pvldb/vol4/p1355-zhao.pdf db/journals/pvldb/pvldb4.html#ZhaoZTC11