Tiers of ontology and consistency constraints in geographical information systems

Consistency constraints placed on a database to assure, that values incorpo rated in the database are consistent, are a well known foundation of Geogra phical Information Systems. Unfortunately in real situations rules for cons istency constraints are not so clear, and inconsistent ontologies are commo n place, not least in geographical information, covering as it does a much wider realm than many other information systems I have suggested elsewhere 5-tiers of ontology for GIS. Such an ontology can integrate different ontol ogical approaches in a unified system. In this paper the relation of the 5- tier ontology and consistency constraints is explored, and it is shown that different constraints are appropriate to different tiers.