College Board-Aligned Original Notes

AP Computer Science Principles Big Idea 2 Topic 1: Data compression

Trace Data compression with small examples before generalizing the pattern.

Big Idea 2: Data. College Board exam weighting listed for this unit: 17%−22% of exam score.

What to Know

Track how variables, objects, lists, or data change step by step.
Watch boundary cases, indexes, loop conditions, and return values.
Use abstraction to hide details only after the behavior is clear.
Always connect this topic back to the larger unit: Data.

Detailed Notes

Data compression is easiest to learn by working through a small concrete example. Write down the input or starting situation, follow each step, and track what changes after every important operation.

In AP Computer Science Principles, AP questions often test whether you understand behavior, not whether you memorized a phrase. You should be able to explain what happens, why it happens, and what output or consequence follows.

Pay close attention to edge cases. In computing, small details such as order of steps, data representation, loop conditions, and assumptions about users can completely change the result.

Key Vocabulary

Data compression

A process for reducing the amount of data needed to represent information.

Algorithm

A finite sequence of steps used to solve a problem.

Iteration

Repeated execution of a set of steps.

Selection

Use of a condition to choose which code or action should run.

Data abstraction

A way to manage complexity by naming and organizing data.

Computing impact

A benefit, harm, or tradeoff caused by a computing innovation.

Quick Practice

How would you explain Data compression in one or two AP-style sentences?

Name the concept, apply it to a specific example or source, and explain the reasoning that connects the evidence to your answer.