Tony Griffiths Alvaro A. A. Fernandes Norman W. Paton Robert Barr The Tripod spatio-historical data model. 23-65 2004 49 Data Knowl. Eng. 1 http://dx.doi.org/10.1016/j.datak.2003.08.003 db/journals/dke/dke49.html#GriffithsFPB04