Project 11G - Translating PDL – Program Design Language into QBASIC Code

How PDL is like a Good Corporate PowerPoint

I've already talked at a high level what Program Design Language (PDL) is. This blog entry is to help those who want to know more, but are too lazy to read a serious work on the subject. PDL is designed to read very much like a high level coding language. In this blog entry, I'll use QBasic code as my example of a high level language (go with me on this, Java-heads). Even though it is soon going to go the way of the dodo, QBasic is still used in education to develop a basic understanding of programming structure.

Both PDL and QBasic share many common words in their lexicons, such as If, Else, End, and Return. PDL coding uses a large vocabulary of keywords that create a natural language fit, such as Assign, Write, Display, Print, Store, Copy, Delete, If, Else, Otherwise, Loop, and While. QBASIC common words include While, Until, For, Next, Goto, If, Then, Input, Loop, and Answer. Though QBasic is a little more rigid and stilting than PDL, in both cases these languages are using common English words to describe how they are carrying out their functions.

As you can see, these two languages are very close in their vocabulary and structure, as if they were two different dialects of Chinese in nearby regions of China. PDL, by design, is a descriptive language that can be used to narrate the algorithms of an application. Once the story of the logic flow is written in PDL, it is a fairly trivial task to re-write PDL into QBasic code to take an application from a theory that it will run well, to a true test of your coding prowess.

Both QBasic and PDL have the same visual format, where lines of code are differentiated in which hierarchy they are involved with through the use of indented text. Both languages have the ability to show comments, which are used to communicate with programmers who will come after the programmer writing the application, telling them what the purpose of each section of code is.

The process of creating PDL code and then translating PDL into QBasic code has its purpose. The narrative nature of PDL forces the programmer to think through the use of variables and ensures that the programmer has planned all of the logic being introduced in the application. This is similar to the way that saying a speech out loud, instead of merely reading it, will uncover errors in grammar simply due to a student hearing the flow of words out loud. Though human readable, a PDL program can’t be compiled and run on a computer. In order to test a section of code that was generated in a PDL environment, it must be run to see if theory meets practice.

Using PDL to explain a QBasic program to yourself and others is similar to creating a PowerPoint presentation for a management group to review a project at work. A project from a technical engineering group may involve a huge amount of technical detail, sometimes with hundreds of pages of settings and configurations, all of which is incomprehensible to a management committee. They need a way of consuming and digesting information that is quickly and easily understandable, so that they can make decisions on allocation of company resources for competing projects, and provide project managers with guidance on company priorities. There is no way someone could take one of these PowerPoint presentations, and go off and configure a complex system with them. They are “manager readable”, just as PDL is “human readable”, designed as a tool for oversight and analysis.