# Use Case: The App's Unit Of Business Logic

> Why a short function deserves its own class.

- URL: https://dantech.academy/en/courses/kotlin-accelerator/engineer-builder/04-clean-architecture-integration/lesson-01-read-domain-use-cases
- Course: [Mobile Action Pro](https://dantech.academy/en/courses/kotlin-accelerator.md)
- Module: Clean Architecture and Integration
- Duration: 11 min
- Difficulty: intermediate
- Access: Enrolled students
- Tiếng Việt: https://dantech.academy/courses/kotlin-accelerator/engineer-builder/04-clean-architecture-integration/lesson-01-read-domain-use-cases.md

## Objectives

- Read a use case with four questions: input, output, dependencies and policy
- Tell a business operation apart from a UI event when naming
- Find where use cases are wired into the app in SharedDomainModule.kt

## In this lesson

1. Lesson Goal
2. Part 1: What Does The "Sign In Use Case" Do?
3. Part 2: What Is The Use Case Base Class For?
4. Part 3: Where Are Use Cases Wired?
5. Part 4: Name It After The Task, Not The UI
6. Code Reading Path
7. Bad Smells
8. Key Takeaways

## Study with an AI agent

The full lesson is for students of this course. Students open the lesson on the web and press **Markdown** to copy all of it, then paste it into Claude, ChatGPT, Cursor or whichever agent you use. Faster: mint a token at `/profile/ai-agents` and your agent reads lessons over MCP.

- [Join the course](https://dantech.academy/en/kotlin-accelerator/checkout)

---

- Previous lesson: [Keep Side Effects Outside The Reducer](https://dantech.academy/en/courses/kotlin-accelerator/engineer-builder/03-state-machine-mvvm/lesson-05-keep-side-effects-outside-reducers.md)
- Next lesson: [Domain vs Data: Where Does Logic Belong?](https://dantech.academy/en/courses/kotlin-accelerator/engineer-builder/04-clean-architecture-integration/lesson-02-separate-repository-contracts-and-data-implementations.md)