danhvb Requirements Modeling Skill
Purpose
Use visual models to clarify and analyze requirements. "A picture is worth 1000 words" - specifically for complex logic and relationships.
When to Use
- Complex logic (State diagrams).
- System interactions (Sequence diagrams).
- Data relationships (Class/ERD diagrams).
- User decisions (Activity diagrams).
Key Modeling Techniques (UML & Others)
1. State Machine Diagram (State Transition)
Use: Object has a complex lifecycle (e.g., Order Status). Elements: States (Rounded Rect), Transitions (Arrows), Events/Triggers.
Example:
stateDiagram-v2
[*] --> Draft
Draft --> PendingApproval: Submit
PendingApproval --> Approved: Manager Approves
PendingApproval --> Rejected: Manager Rejects
Rejected --> Draft: Edit
Approved --> [*]
2. Sequence Diagram
Use: Interaction between systems or objects over time. Elements: Participants (Lifelines), Messages (Arrows).
Example:
sequenceDiagram
User->>Frontend: Click Login
Frontend->>Backend: POST /login
Backend->>Database: Validate User
Database-->>Backend: User OK
Backend-->>Frontend: Token
Frontend-->>User: Dashboard
3. Activity Diagram
Use: Workflow logic (similar to Flowcharts but supports parallelism). Elements: Activities, Decisions, Forks/Joins.
4. Class Diagram
Use: Conceptual data modeling (Object-Oriented). Elements: Class boxes (Name, Attributes, Operations).
5. Decision Tables
Use: Complex business rules with many conditions. Format: Conditions vs. Actions.
| Condition: Age < 18 | Y | Y | N | N | | Condition: Member | Y | N | Y | N | | Action: Discount| 50% | 20% | 10% | 0% |
Best Practices
- Model for Audience: Don't show a Sequence Diagram to a marketing VP. Use Flowcharts for business, UML for devs.
- Keep it Simple: Break complex diagrams into smaller views.
- Validate with Code: Ensure the model matches reality (or feasible reality).
- Annotate: Add notes to explain "Why".
Tools
- Mermaid: Text-to-diagram (Great for docs).
- PlantUML: Standard text-based UML.
- Lucidchart / Visio: Visual drag-and-drop.
- Figma: Good for high-level flows.