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Boundarieslntersect 
If more than one boundary, 
Check that no two 
boundaries intersect 
OBJECT METHOD METHOD INPUT METHOD ACTION GETS VALUE BY 
THE METHOD 
Association CheckComponent ComponentDomain Check that component 2 
Object Component is member of 
ComponentDomain 
Aggregation CheckComponent ComponentDomain Check that component - 
Object Component is member of 
ComponentDomain 
Point XYZ coordinate values Assign values to X, yz 
attributes 
LineString StartPoint Set of points Assign values to se 60 
EndPoint (association of attributes D. op, Ip 
IntermediatePoint points) 
Intersectsltself Check that line string does 
not intersect itself 
Connected ClosingBoundary Instance(s) of Determine order outer. boundary 
Area OuterBoundary LineString class between boundaries inner. boundary 
InnerBoundary 
  
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AreasDisjoint 
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check that areas 
component_area 
  
Area ConnectedArea are distinct 
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NullArea ConnectedArea or with two ap areas; ap line 
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class 
  
  
  
one outer boundary; 
  
  
  
  
Figure 4. The methods that enforce the implicit integrity of object classes. 
4.3 SPECIFICATION OF SOME EXPLICIT 
CONSTRAINTS ON GEOMETRICAL OBJECT TYPES 
The geometrical object model that is represented in 
this paper consists of geometrical object classes along 
with methods that enforce the structural integrity of 
the classes. The model depicted in Figure 1 is static in 
the sense that it does not provide modelling constructs 
that make it possible to constrain the spatial 
relationships between the geometrical object types. 
This study is based on the assumption, that in a 
geographical database it should be possible to specify 
user defined, arbitrary constraints on the object classes. 
The fact that some constraints on geographical objects 
are heavily application dependent, has the following 
461 
consequences: It is the application database designer 
who knows best what the constraints on database 
should be. These constraints don't need to be, or 
rather, they should not be included implicitly in the 
data model, because all of them might not be needed in 
an application, and thus their enforcement would 
cause unnecessary processing overhead. Rather, 
constraints that are typical to a certain application 
should be specified as explicit constraints. 
Next, the model depicted in Figure 1 is extended by 
modelling constructs that make it possible to specify 
explicitly user-defined constraints on object classes 
whose semantics are derived from the spatial 
relationships between objects. Such modelling 
constructs could be modelling methods of the