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3.4 SYSTEM ARCHITECTURE 
3.4.1 Traditional Architectures for Information Systems 
Since a GIS is a special case of an information system, GIS architectures may be built around the proven 
ANSI/SPARC three level architecture first developed for database systems (e.g. Korth and Silberschatz, 1991). An 
overview of the architecture is given in Figure 3. A single conceptual data model is mapped onto several external 
views which each present a subset of the conceptual view. 
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Figure 3: The ANSI/SPARC three level database architecture (Korth & Silberschatz, 1991). 
3.4.2 A Modified Architecture for a Feature-Based GIS 
The architecture of an integrated GIS depends greatly on the concepts that are to be presented to the user. If the only 
means of interaction is via the concept of features, then the architectural issues can be managed according to the 
design in Figure 4. Only the transforms from image data to features must be supported, since the user only operates 
on the feature view. 
This 
integi 
discu: 
Figure 4: An architecture for an integrated, feature oriented GIS 
This design is discussed in detail in Gahegan (1994a) and Gahegan & Flack (1996). Since the user interacts via 
features only, the role of the conceptual layer is simply to provide the functionality of a GIS to the various external 
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