Regardless of the documentation effort, the true meaning of the code is hidden in the source statements. The purpose of the documentation is to make it possible to understand the state of the code and its intent. The program design language or PDL attempts to bridge the gap between code writer and code reader. PDL is also called pseudo-code. The idea of PDL is that we will stay out of the syntactic rules of an implemented programming language but maintain a limited vocabulary of terms to be sure too much magic doesn't find its way into the design. PDL is used for the design aspects of construction.
For the most part, programming languages differ little between languages of the same types. For example, imperative style languages (such as C and C++ and Pascal) have a command style of presentation. These languages use verbs to signify action and a few special ideas, like if or while to signify control. We specifically want to use English as much as possible. The problem with PDLs is finding a good level to write at. The PDL should make the exact coding quite obvious. Good PDL should also make the overall concepts of the routine obvious to the reader.
While we don't want to emulate code, we don't want to keep re-inventing terminology that is suggested by the system being implemented. For example, the name NIL or NULL means just about the same thing everywhere in computer science. It would be silly to invent a new, unfamiliar name. There is a fine line between these two requirements.
Some ideas about good PDL are given in Figure 9. The true professional writes documentation that has the look and feel of a textbook. If you are uneasy about how to say things or how something might best be explained, go to a high quality textbook in the area and see how the authors discuss similar concepts.
Table 10: Constructing a Routine
