Specifying and Implementing Constraints in GIS - with Examples from a Geo-Virtual Reality System

Constraints are important elements of every modelling process, but until now they have been treated in an ad hoc manner, depending on the specific application domain and the capabilities of the tools used. In GIS and GeoVR applications, constraints are conditions which always have to be valid (true) within the model populated with real geographic object instances. This paper argues that constraints should form a systematic part of the object class definition, similar to other aspects of the definition, viz. attributes, methods and relationships. Also, the implementation of constraints in all GIS and GeoVR subsystems (at front-end, database and exchange (I/O) level) should be derived automatically from the constraints specified by the framework. The paper therefore puts forward a framework for modelling constraints comprising (1) a classification and clarification of constraints, (2) a formal description using the unified modelling language/object constraint language (UML/OCL) and (3) implementation characteristics. The components of the framework are illustrated and applied to SALIX-2, a geo-virtual reality (GeoVR) landscape modelling system. GeoInformatica (2006) 10: 531–550 DOI: 10.1007/s10707-006-0345-5 J. Louwsma Waterschap Roer en Overmaas, Parklaan 10, 6131 KG Sittard, The Netherlands e-mail: [email protected] S. Zlatanova : P. van Oosterom GIS Technology Research Group, Delft University of Technology, Jaffalaan 9, 2628 BX Delft, The Netherlands S. Zlatanova e-mail: [email protected] P. van Oosterom e-mail: [email protected] R. van Lammeren (*) Centre for Geo-Information, Wageningen University, P. O. Box 47, 6700 AA Wageningen, The Netherlands e-mail: [email protected]