a Mix-in is a special class in that it cannot be instantiated and it is not visible in the Knowledge Fusion navigator. The class inherits the attributes of the mix-in class. A mix-in class is so named because its definition is "mixed-in" with the definition of a new class. The mix-in capability can be used to manage geometric and non-geometric rule sets in separate files, combining them as needed. Any logical grouping of a set of rules can be made and managed by placing related rules in their own class to be used as a mix-in. You may have zero, one, or more mix-in classes. Each mix-in class is delimited by a space (mixin_1 mixin_2). In our example, ug_base_part is the mixed-in class.

Knowledge Fusion allows you to customize a class hierarchy with your own mix-ins. This allows you to add rules to all classes without editing each class. To use this feature, you copy any one of the following common kernel DFA files from the kernlib directory to your own local DFA files directory:

• globalvariablesmodifier.dfa

• nulldesignmodifier.dfa

• basedesignmodifier.dfa

• worldmodifier.dfa

To add your own rule, you edit the local copy of this file and add your data to it. For example, if you wanted to have the following attribute available to all your classes, then copy the following to basedesignmodifier.dfa:

(Number Parameter Modifiable ) Serial_Number: 0; # Company specific identifier