AN OBJECT-ORIENTED GEOGRAPHIC INFORMATION-SYSTEM SHELL

Geographic Information Systems (GIS) combine the requirement for graphical display of information with the requirement to manage complex, disk-based data. The object-oriented approach is recognized as an appropriate technology for meeting both of these requirements, and several attempts have been made to build a GIS using object-oriented data management systems. The paper considers the design of a GIS shell by extension of an object-oriented (database) system. A GIS shell does not include any application-specific objects, but extends a basic object-oriented system to provide spatial objects with appropriate behaviour. The starting point for this work was the set of requirements of users of an existing GIS shell. Central objectives are to provide multiple views of application objects, with independence from the stored representation of the spatial attributes. The paper discusses the principles employed in the design of the shell, and a 4-level architecture for organizing shell objects so as to meet the stated objectives. Implementation issues relating to the appropriateness of an object-oriented database management system are discussed towards the end of the paper.