**Different types of information units of CAD**

There are different types of information units defined. They are :

Class 0

The geometric primitives needed for describing 2- and 3-dimensional objects such as points, lines, circles, parabolas, planes and surfaces.

Class 1

Complex geometric entities for defining complex curves, complex solids, shells, faces and so on.

Class 2

Graphical aids to map product information onto technical presentations. These aids include view block definitions, block definitions, line fonts, cross hatching, characters for defining symbols and so on.

Class 3

Grouping mechanisms to assist the mathematical operations needed for the manipulation of the design objects. Typical representations are coordinate transformations, scalar series, general matrices, tabulated functions, physical quantities, material properties and so on.

Class 4

Descriptive aids to represent diameters, angles, labels, text, cross-hatching, surface finishes and so on.

Class 5

Elements defining the structural relations such as calling block, group, attribute and homogeneous entities.

Class 6

Connecting elements to describe logic between the elements of any class.

Class 7

FEM elements to build the FEM model. Typical elements are finite elements, model for an element, computations, definition of a computation, loads, damping, Eigenvalue, knot renumbering and so on.

Class 80

Gives the user the possibility of defining his own elements.

Class 99

Management aids to structure SET files. They include SET header, ensemble header as well as 'End' specifier for an ensemble and a 'SET'.