A line is stored as a reference to two 'node' endpoints and a reference to
a line type (e.g. straight line, circular arc, circle, smooth curve).
A surface consists of one or more line primitives which form together a
closed polygon. One exterior and several interior boundaries are possible
for the same primitive.
i | A TIN is a hybrid type of primitive. It contains a list of references to
HU adjacent triangle primitives, to the three nodes belonging to the corners
of the triangle and the surface normals at these points.
b) Features
A feature is a model of a real-world geographic element in the database.
It is defined by a set of geometric primitives which in turn can be de-
fined by other primitives. Features stored at the project level are
consistent with the topologic type (e.g. all 'surfaces' are closed
polygon) and topologically correct with respect to other features
against which they are checked (e.g. no buildings on roads).
c) Complex features
Complex features are used to define an entity in terms of one or more
other features. For example the complex feature 'parcel' could consist
of the features 'parcel boundary', 'house' and 'garage'. The user can
directly extract the entire content of a single or complex feature.
d) Feature class
The feature classification defines the logical organisation of the data.
Topographic checks can be defined between elements of different feature
classes. The topology of features is unique for a feature class and
classes are also represented identically on a graphic display. A feature
class can have subclasses, e.g. the feature class 'buildings' can have
subclasses with 'single-storey buildings', 'two-storey buildings', etc.
e) Partition
A partition is a working subset of a project. Users interact with the
system at this level to capture, edit, update and manipulate data.
Partitions are extracted from a project by means of a partition defini-
tion, which describes the selection of feature classes and how they
will be presented, the security restrictions and the spatial extent.
f) Project
The definitive version of the database is held in the project and is
updated when a partition is merged with a project. Each project can
have several partitions. Feature classifications with the definition
of attributes including range checking, topographic and topologic
checks, partitions, graphic transforms and restrictions on operator-
group access are created and maintained at this level.
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