computer science

Use case diagram

Use case diagram 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 Use case diagram rather than just read about it. In short: A use case diagram is a graphical depiction of a user's possible interactions with a system. A use case diagram shows various use cases and different types of users the system has and will often be accompanied by other types of diagrams as well.

Key takeaways

Use case diagram 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 Use case diagram to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Use case diagram from memory before moving on to harder problems.

Reference excerpt

A use case diagram is a graphical depiction of a user's possible interactions with a system. A use case diagram shows various use cases and different types of users the system has and will often be accompanied by other types of diagrams as well. The use cases are represented by either circles or ellipses. The actors are often shown as stick figures.

Application While a use case itself might drill into a lot of detail about every possibility, a use-case diagram can help provide a higher-level view of the system. It has been said before that "Use case diagrams are the blueprints for your system". Due to their simplistic nature, use case diagrams can be a good communication tool for stakeholders. The drawings attempt to mimic the real world and provide a view for the stakeholder to understand how the system is going to be designed. Siau and Lee conducted research to determine if there was a valid situation for use case diagrams at all or if they were unnecessary. What was found was that the use case diagrams conveyed the intent of the system in a more simplified manner to stakeholders and that they were "interpreted more completely than class diagrams".

See also Agile software development Business case Fundamental modeling concepts Object Process Methodology SysML Unified Modeling Language User story

References

Bibliography Gemino, A., Parker, D.(2009) "Use case diagrams in support of use case modeling: Deriving understanding from the picture", Journal of Database Management, 20(1), 1–24. Jacobson, I., Christerson M., Jonsson P., Övergaard G., (1992). Object-Oriented Software Engineering – A Use Case Driven Approach, Addison-Wesley. Kawabata, R., Kasah, K. (2007). "Systems Analysis for Collaborative System by Use Case Diagram", Journal of Integrated Design & Process Science, 11(1), 13–27. McLaughlin, Brett D.; Pollice, Gary; West, David (December 1, 2006). Head First Object Oriented Analysis and Design. Shroff Publishers & Distributors Pvt Ltd. ISBN 978-8-184-04221-4.

Illustrations

Worked examples

Example 1 — a first encounter with Use case diagram

Start with the simplest possible case. Write down what Use case diagram 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 Use case diagram 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 Use case diagram 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 Use case diagram

In research: Use case diagram 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 Use case diagram 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: Use case diagram is common in secondary-school and first-year university syllabi. It links to neighbouring topics Software project management, Software requirements, Systems Modeling Language, so understanding it makes those chapters shorter.
In everyday life: Look for Use case diagram 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 Use case diagram in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Use case diagram 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 Use case diagram out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Use case diagram in simple terms?

Why does Use case diagram 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 Use case diagram?

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 Use case diagram.