Virtual Realms : An E cient ImplementationStrategy for Finite Resolution Spatial Data

A realm is a planar graph over a nite resolution grid that has been proposed as a means of overcoming problems of numerical robustness and topological correctness in spatial database systems. While the realm structure and the spatial algebra that is associated with it provide a range of desirable facilities for modelling spatial information in database systems, widespread exploitation will only be practical if eecient implementation strategies are identiied. This paper shows how data types can be supported eeciently over virtual realms, where the nite resolution grid is not stored explicitly, but is generated only partially and as needed. This approach avoids the considerable storage space overheads associated with the original proposal for the implementation of realms, and provides overall runtime performance that often improves upon that of less space eecient implementation strategies.