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.