Myung Keun Shin Soon-Young Huh Donghyun Park Wookey Lee Relaxing Queries with Hierarchical Quantified Data Abstraction. 47-61 2008 19 J. Database Manag. 4 http://www.igi-pub.com/articles/details.asp?ID=8338 db/journals/jdm/jdm19.html#ShinHPL08