title: the mlpq/gis constraint database system. authors: yuguo liu , yiming li , pradip kanjamala , rui chen , yonghui wang , peter z. revesz. venue: sigmod conference. year: 2000
title: the ccube constraint object-oriented database system. authors: alexander brodsky , victor e. segal , jia chen , paval a. exarkhopoulo. venue: international conference on management of data. year: 1999