# Use Case Analysis

## About

**Use Case Analysis** is the process of **identifying, describing, and understanding how users or other systems interact with our system** to achieve specific goals.\
In **System Design**, it helps bridge the gap between **business needs** and **technical implementation** by turning high-level requirements into **practical interaction scenarios**.

Think of it as a **storyboard for our system**—showing who uses it, what they do, and how the system responds.

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In System Design, use case analysis ensures that our architecture isn’t just technically sound—it’s aligned with **how people and systems will actually use it**.
{% endhint %}

## Why It Matters in System Design ?

1. **Clarifies Functional Requirements**
   * Helps ensure that all necessary features and interactions are captured before designing the architecture.
2. **Identifies Edge Cases Early**
   * Forces us to think about alternative flows, error scenarios, and unusual usage patterns.
3. **Aligns Business & Technical Teams**
   * Product managers, designers, and engineers can all refer to the same use case document.
4. **Supports Test Planning**
   * Test cases can be derived directly from use cases, ensuring coverage for critical flows.
5. **Informs Design Decisions**
   * Understanding how a system will be used helps us choose the right architecture, scaling strategy, and data model.

## The Use Case Analysis Process

### **1. Identify the Actors**

Actors can be:

* **Primary actors** – Directly interact with the system (e.g., user, admin, mobile app).
* **Secondary actors** – Provide services to the system (e.g., payment gateway, notification service).

**Example**\
For an e-commerce checkout flow:

* Primary actor: Shopper
* Secondary actor: Payment processor, inventory service

### **2. Define the Goal**

Clearly state **what the actor wants to achieve** in this interaction.

* Keep it simple and user-focused.

**Example**\
Goal: “Complete a purchase and receive confirmation.”

### **3. Describe the Main Success Scenario**

Step-by-step outline of **how the interaction proceeds when everything works as intended**.

**Example**

1. Shopper adds items to cart.
2. Shopper proceeds to checkout.
3. System displays order summary.
4. Shopper enters payment details.
5. Payment is processed successfully.
6. System confirms the order and sends email confirmation.

### **4. Document Alternative Flows**

Not every interaction is perfect—document **variations and optional paths**.

**Example**

* Shopper updates the shipping address mid-checkout.
* Shopper uses a coupon code.

### **5. Capture Exception Scenarios**

Identify **failure cases** and how the system responds.

**Example**

* Payment fails due to insufficient funds → System prompts user to retry or choose another payment method.
* Item goes out of stock before checkout → System alerts user and updates the cart.

### **6. Specify Preconditions and Postconditions**

* **Preconditions** – What must be true before the use case starts.\
  Example: User must be logged in.
* **Postconditions** – What will be true after the use case completes successfully.\
  Example: Order is stored in the database, and inventory is updated.

### **7. Validate with Stakeholders**

Review use cases with:

* Product managers (to confirm business logic)
* Engineers (to confirm technical feasibility)
* QA testers (to ensure testability)

## Best Practices

* Use **clear, simple language -** avoid overly technical terms in the main scenario.
* Keep use cases **solution-agnostic**; focus on *what* the system does, not *how* it’s implemented.
* Number the steps for easy reference.
* Don’t skip **failure scenarios -** they often have huge design implications.


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