Use simplified representations in top-down and bottom-up design approaches to conceptualize your design and to simplify the representation of complex assemblies. When you use a top-down design approach, you create space claims called envelopes for components in an assembly. You build the detailed parts and subassemblies to fit the envelopes. For example, you might create envelopes for the engine, transmission, and many other complex subassemblies in an automotive design. As each team creates detailed designs of its subassembly, you can substitute the fully detailed subassembly for the corresponding envelope.

When you use a bottom-up approach, you start with a complex assembly and simplify it. One simplified representation could act as a design's table of contents by substituting a lower-level simplified representation for each subassembly. Another simplified representation might exclude portions of the design to focus on specific areas.