You can create hierarchies
of object classes. When you base a new object class on an existing
object class, the new object class has all the properties of the base
You cannot change base
properties, but you can modify their attributes, including the default
value and the range of allowable values, and you can include additional
- Define an object class called Roads with
the basic properties that you want to assign to all roads.
- Define object classes called Primary
Roads, Local Roads, and Fire Roads, and base each of them on Roads.
Because the new object
classes are based on Roads, they include all the properties selected
When you select all objects
in a base class, objects in object classes based on that class are
Using Object Classes as
Base Classes Only
Sometimes when you create
a base class, you intend to use it only as a base for other object
classes and not to create objects in drawings. For example, you
may not want the to use the Roads object class to create roads.
You want people to create roads using the Primary Roads and Secondary
Roads classes that are based on the Roads class. You can specify
that an object class can be used only as a base class.
Editing Base Classes
To edit a definition
for an object class, you must have a sample object in the drawing.
However, if you use an object class as a base class only, you will
not have any example objects. For these object classes, you must
edit the .xml definition file directly.