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### Primitive Objects

We model three basic types of geometric objects (see Figure 2):

• Regions have to be convex, connected and without holes.
• Lines and arrows must not be self-intersecting, are either circular or directed, and have exactly two end points.
• Points are elements of lines and describe their start or end points.

We need a fourth type of geometric object which is basically treated as a 2D extent type:

• Text: The minimal bounding box of the text string is defined as a region representing the text element.

Every object consists of its boundary and its interior. The boundary of a point is an empty point-set, the boundary of a line is either an empty point-set (for a circular line) or a point-set consisting of its two end points (for a non-circular line). The boundary of a region is a circular line. The interior of an object is the object without its boundary. In case of points and circular lines their interior is identical to the object itself.

Figure 2: Basic vocabulary

Volker Haarslev
Wed Jan 31 15:50:43 MET 1996