Reference objects represented by a
bounding box or another kind of "spatial envelope" that encloses its borders, can be denoted with the maximum number of
dimensions of this envelope: '0' for
punctual objects, '1' for
linear objects, '2' for
planar objects, '3' for
volumetric objects. So, any object, in a
2D modeling, can by classified as
point,
line or
area according to its delimitation. Then, a
type of spatial relation can be expressed by the class of the objects that participate in the relation: •
point-point relations: ... •
point-line relations: •
point-area relations: •
line-line relations: •
line-area relations: •
area-area relations: More
complex modeling schemas can represent an object as a composition of
simple sub-objects. Examples: represent in an
astronomical map a star by a
point and a
binary star by
two points; represent in
geographical map a river with a
line, for its
source stream, and with an strip-
area, for the rest of the river. These schemas can use the above classes, uniform composition classes (
multi-point,
multi-line and
multi-area) and heterogeneous composition (
points+
lines as "object of dimension 1",
points+
lines+
areas as "object of dimension 2"). Two internal components of a
complex object can express (the above)
binary relations between them, and
ternary relations, using the whole object as a
frame of reference. Some relations can be expressed by an abstract component, such the
center of mass of the binary star, or a center line of the river. == Temporal references ==