ABSTRACT
Peter van Oosterom GIS-technology Section, Delft University of Technology, Delft, The Netherlands
7.1 Introduction Constraints are important in every GI modelling process but until now have received only ad hoc treatment, depending on the application domain and the tools used. In a dynamic context, with constantly changing geo-information, constraints are very relevant; any changes arising should adhere to specified constraints, otherwise inconsistencies (data quality errors) will occur. In GIS, constraints are conditions that must always be valid for the model of interest. This chapter argues that constraints should be part of the object class definition, just as with other aspects of that definition, including attributes, methods and relationships. Furthermore, the implementation of constraints (whether at the front-end, database level or communication level) should be driven automatically by these constraints’ specifications within the model. But, this is not possible yet, so this chapter will describe some implementation steps as interactively executed.
