1. Barnett, L. and Carlis, J. C. (1993). “Feature information support and the SDTS conceptual data model: clarification and extension”, in Proceedings of the AUTOCARTO 11. Minneapolis, pp. 132-144.
2. Bucher, F., Stephan, E.-M. and Vckovski, A. (1994). Integrated analysis and standardisation in GIS, in Proceedings of the Twelfth European Conference on Geographical Information Systems. Paris, pp. 67-75.
3. Missing information (applicable and inapplicable) in relational databases