13.1 LESSON FROM THE REAL WORLD: THE MANAGER’S PERSPECTIVE AND THE ENGINEER’S PERSPECTIVE
The views of a library can be thought of as the projections of an item from various points of view. This is similar to the old puzzle-book question of describing what sort of object can cast a shadow that looks like a circular from one side, a square from another side and a triangle from yet another side. Figure 13.1 gives the answer. In terms of libraries, the views that are involved are those that are used by the various engineering design automation (EDA) tools. Each tool has a need for various parts of the description of the elements of the library, but no particular tool needs to care about all the aspects of the library. However, it is important to the success of any design that would use such a library that the various views tend to describe consistent aspects of the library. In the case of the puzzle-book question, the projections tend to be orthogonal of each other. As a result, the shape of one shadow tends to have little consequence to the shape of the other shadows but does have consequence for the actual shape of the object in the figure. In the case of the various views of a library element, the views may not be so orthogonal. A slight change in one view—say, the liberty file description—may require substantial change in one or more of the other views—for instance, the Verilog description.