4.2.2.2 Class and Object Hierarchy

Classes and subclasses may incorrectly imply an object hierarchy. For example the fact that RIB is a subclass of MATERIAL may imply that a material object would be the parent of a rib object. This is not the case. The class/subclass structure is used merely as a means to inherit necessary properties in the definition of another class. At no time during PIMES processing will there be a feature attached to a material object.

Figure 28 illustrates how the class description hierarchy may differ from the connections of objects at run time. It is important to note that the way classes and subclasses are arranged do not necessarily denote the connection of objects during run time. If this were so, the FEATURE class would be a subclass of PART. This is not the case because there are properties in the PART class, such as part_width, which the class FEATURE has no use for.

There are some common properties, such as minimum draft, of which value a particular feature object, a rib for example, may wish to inherit from its parent. Both PART and RIB both have been imbued with this property by the MATERIAL class. During run time, however, only the part object is attached to a material object. The part inherits the value directly from the material object. The rib object is attached to the parent, thereby obtaining its value from the parent.

Figure 28 Class Hierarchy and Run Time Objects