Shashi Shekhar Ranga Raju Vatsavai Sanjay Chawla Thomas E. Burk Spatial Pictogram Enhanced Conceptual Data Models and Their Translation to Logical Data Models. 77-104 http://link.springer.de/link/service/series/0558/bibs/1737/17370077.htm 1999 conf/isd/1999 Integrated Spatial Databases db/conf/isd/isd1999.html#ShekharVCB99