Attempts to achieve the same kind of design system for Mechanical CAD have proven much more difficult. There are several reasons for this.
Mechanical functions are more complex and difficult to classify.
There is much more variety in the ways mechanical functions are commonly implemented. Consider, for example, the number of methods commonly used to attach two parts. The implementations of functions are not usually distinct. In good VLSI design and software design, each distinct function is usually implemented by a clearly delineated portion of the final product. Often doing this introduces some redundancy and inefficiency into the design, but this is a small cost to pay for conceptual simplicity.