connection, message, and a few others for which an icon is obviously inappropriate. For example, a kb-workspace has no icon: its visual representation is the workspace itself. When a class has an iconic representation, the Icon-description attribute of its definition specifies the icon that represents an instance of the class. The default value of Icon-description is inherited. The
Icon-description attribute is a special case. It could appear as an initializable system-defined attribute, but an icon description can be very long and complex: including it with other attribute initializations could make the other attributes difficult to access. Making Icon-description a separate attribute prevents such problems, with the side-effect that the attribute appears in every definition whether or not the defined class has an iconic representation. When a class has no iconic representation, the Icon-description attribute of its definition cannot be edited and has no effect.
logical-parameter as one of the direct-superior-classes, and no other icon has been defined through another class, the icon for class instances will look like this.
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You can replace the default, system-defined icon with your own design by editing the icon in the Icon Editor. Most user-defined icons represent objects used for knowledge representation. For example, you may wish to draw a car icon to represent
automobile objects, a book icon for a help object, or a rocket icon for space-vehicle objects. You can also define icons for user-defined subclasses of G2 components, such as procedures or image definitions.
Hint: G2 includes many sample icons in the kbicons.kb module, located in the kbs subdirectory of the G2 product directory.
Icon Inheritance
The icon that a class inherits depends on its class inheritance path. For a detailed explanation of the class inheritance path, see Chapter 13, Classes and Class Hierarchy.
A class inherits the first explicitly-defined (rather than inherited) icon-description that G2 locates on the class inheritance path, which may be a user- or a system-defined icon. The next diagram presents an example of a class inheriting a user-defined icon, or a system-defined icon, depending on which way the direct superior classes are specified.
CIRCLE superior class, with an instance, circle-1. The two other definitions, CIRCLE-CHILD and VARIABLE-CIRCLE, display their direct superior classes attribute. Both of these classes have instances with different icons, illustrating how an icon is inherited through the class inheritance path.
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Using the Icon Editor
The Icon-description attribute describes an icon textually, using a graphical description language. However, icons are rarely specified by typing in their descriptions. 
To create a new icon for a definition:
Use the Icon Editor to define the icon graphically.
Icon-description attribute with a description corresponding to the icon you defined. For a complete description of the Icon Editor, and of the text syntax for the
Icon-description attribute, see Chapter 37, The Icon Editor and Icon Management.
Icon Library
A library of prefabricated icons is available in kbicons.kb in the G2 demos directory, as described under Demonstration KBs.