computer science

Program Design Language

Program Design Language is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Program Design Language rather than just read about it. In short: Program Design Language (or PDL, for short) is a method for designing and documenting methods and procedures in software. It is related to pseudocode, but unlike pseudocode, it is written in plain language without any terms that could suggest the use of any programming language or library.

Key takeaways

Program Design Language belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Program Design Language to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Program Design Language from memory before moving on to harder problems.

Reference excerpt

Program Design Language (or PDL, for short) is a method for designing and documenting methods and procedures in software. It is related to pseudocode, but unlike pseudocode, it is written in plain language without any terms that could suggest the use of any programming language or library. PDL was originally developed by the company Caine, Farber & Gordon and has been modified substantially since they published their initial paper on it in 1975. It has been described in some detail by Steve McConnell in his book Code Complete.

Worked examples

Example 1 — a first encounter with Program Design Language

Start with the simplest possible case. Write down what Program Design Language claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Program Design Language before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Program Design Language ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Program Design Language

In research: Program Design Language appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Program Design Language in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Program Design Language is common in secondary-school and first-year university syllabi. It links to neighbouring topics Algorithm description languages, Software engineering stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Program Design Language outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Program Design Language in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Program Design Language means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Program Design Language out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Program Design Language in simple terms?

Why does Program Design Language matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Program Design Language?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Program Design Language.