The life cycle of a mechanical component from its first conceptualization to its final packaging involves many intermediate processes such as product definition, engineering analysis, manufacturing planning, material procurement, and production control. These processes, of course, can be further broken down to finer steps or operations, but what is important to note is how these processes interact. For example, results from engineering analysis may necessitate changes in the initial product definition. High cost in manufacturing also brings about modifications in manufacturing planning. Consequently, it is more efficient and effective to have a central description of the object or product for the purposes of reference, modification, manipulation, and further processing. This is the basic motivation for shape description and modeling in digital computers.