Shashi Shekhar Sanjay Chawla Sivakumar Ravada Andrew Fetterer Xuan Liu Chang-Tien Lu Spatial Databases - Accomplishments and Research Needs. 45-55 1999 11 IEEE Trans. Knowl. Data Eng. 1 http://www.computer.org:80/tkde/tk1999/k0045abs.htm db/journals/tkde/tkde11.html#ShekharCRFLL99