@Inproceedings{Lorentzos99,
author = {Lorentzos, N. A. and Tryfona, N. and Viqueira, J. R.},
title = {Relational Algebra for Spatio Data Management},
booktitle = {Proceedings of the International workshop on Integrated Spatial Databases, Digital Images and GIS (ISD'99) - LNCS 1737},
address = {Portland, OR},
year = {1999},
pages = {192-208}
}