What is the difference between horizontal and vertical module organization?

Question

Accepted Answer

**Horizontal** — organize by layer. **Vertical** — organize by feature.

**Horizontal (Layer-Based):**
- Group by technical layer.
- controllers/, services/, models/.
- Clear technical separation.
- Hard to find feature code.

```
Horizontal:
src/
  controllers/
    userController.js
    orderController.js
  services/
    userService.js
    orderService.js
  models/
    userModel.js
    orderModel.js
```

**Vertical (Feature-Based):**
- Group by feature.
- user/, order/, payment/.
- Feature code together.
- Easier to maintain.

```
Vertical:
src/
  user/
    controller.js
    service.js
    model.js
  order/
    controller.js
    service.js
    model.js
```

**Key differences:**
- **Horizontal** — by layer.
- **Vertical** — by feature.
- **Horizontal** — technical.
- **Vertical** — business.

Systems Analyst: What is the difference between horizontal and vertical module organization?