Object Object 
Method 
  
S iuMessage 
  
  
  
  
Encapsulation 
  
  
Figure 2 : The object-oriented approach. 
  
      
    
    
  
Contra- 
dictionary 
knowledge 
    
  
Implicit description in GIS Explicit description in GIS 
  
  
Figure 3 : Various types of knowledge. 
  
Conventional systems Knowledge-based systems 
  
  
Problem solving 
strategy 
Algorithms 
  
Domain 
specific 
knowledge 
  
  
Data base Data base 
  
  
  
  
  
  
  
  
  
Figure 4 : Conventional versus knowledge-based systems architecture. 
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