# C4 Model Guidelines

## Overview

The C4 model is a hierarchical approach to visualizing software architecture through four levels of abstraction.

## Level 1: System Context Diagram

- **Purpose**: Shows how the system fits into the world around it
- **Audience**: Technical and non-technical people
- **Elements**: Users, software systems, external systems
- **Key Questions**:
  - Who uses the system?
  - What external systems does it interact with?
  - What are the main user goals?

## Level 2: Container Diagram

- **Purpose**: Zooms into the system boundary, showing high-level technical building blocks
- **Audience**: Software developers and architects
- **Elements**: Containers (applications, databases, file systems, etc.)
- **Key Questions**:
  - What are the main functional areas?
  - What technology choices have been made?
  - How do containers communicate?

## Level 3: Component Diagram

- **Purpose**: Zooms into a container to show the components within it
- **Audience**: Software developers
- **Elements**: Components, interfaces, data models
- **Key Questions**:
  - What are the main components?
  - How do components interact?
  - What are the key interfaces?

## Level 4: Code Diagram

- **Purpose**: Zooms into a component to show how it is implemented
- **Audience**: Software developers
- **Elements**: Classes, interfaces, packages
- **Note**: Usually created using UML or similar tools

## Best Practices

### Naming Conventions

- Use clear, descriptive names
- Be consistent across all diagrams
- Use business terminology where appropriate
- Avoid technical jargon in context diagrams

### Relationship Labels

- Use active voice ("Uses", "Sends data to")
- Be specific about protocols and technologies
- Include data flow direction
- Use consistent terminology

### Diagram Layout

- Use autolayout for consistency
- Group related elements
- Minimize crossing lines
- Use appropriate colors and styling

### Technology Choices

- Be specific about technologies
- Justify technology decisions
- Consider scalability and maintainability
- Document technology constraints

## Common Anti-Patterns

### Context Diagram

- ❌ Too many external systems
- ❌ Missing key users
- ❌ Unclear relationships
- ❌ Technical details in context diagram

### Container Diagram

- ❌ Too many containers
- ❌ Missing communication protocols
- ❌ Unclear responsibilities
- ❌ Missing security boundaries

### Component Diagram

- ❌ Too much detail
- ❌ Missing interfaces
- ❌ Unclear data flow
- ❌ Missing error handling

## Structurizr DSL Best Practices

### Workspace Structure

```dsl
workspace "Name" "Description" {
    model {
        // All model elements
    }
    views {
        // All views
    }
}
```

### Element Definitions

- Always provide descriptions for elements
- Use consistent naming conventions
- Group related elements logically
- Apply appropriate tags and properties

### Relationship Definitions

- Use descriptive labels
- Include technology information
- Specify data flow direction
- Avoid circular dependencies

### View Configuration

- Use autolayout for consistency
- Include all relevant elements
- Apply appropriate themes
- Test view layouts

## Quality Checklist

### Context Diagram

- [ ] All key users are represented
- [ ] All external systems are identified
- [ ] Relationships are clearly defined
- [ ] Technology choices are appropriate
- [ ] Diagram is understandable to non-technical stakeholders

### Container Diagram

- [ ] All major components are represented
- [ ] Technology choices are justified
- [ ] Data flow is clear
- [ ] Security boundaries are defined
- [ ] Scalability considerations are addressed

### Component Diagram

- [ ] All major components are represented
- [ ] Interfaces are clearly defined
- [ ] Data flow is logical
- [ ] Dependencies are minimal
- [ ] Error handling is considered

## Common Issues and Solutions

### Issue: Too Many Elements

**Solution**: Focus on the most important elements and relationships. Use multiple diagrams if needed.

### Issue: Unclear Relationships

**Solution**: Use descriptive labels and include technology information. Show data flow direction.

### Issue: Inconsistent Naming

**Solution**: Establish naming conventions and apply them consistently across all diagrams.

### Issue: Missing Context

**Solution**: Ensure each diagram level provides appropriate context for its audience.

### Issue: Technical Details in Context Diagram

**Solution**: Keep context diagrams high-level and business-focused. Move technical details to container diagrams.

## Integration with Development Process

### Planning Phase

- Create context diagrams to understand system scope
- Use diagrams for stakeholder communication
- Validate requirements against architecture

### Design Phase

- Create container diagrams for technical design
- Use component diagrams for detailed design
- Validate design decisions

### Implementation Phase

- Keep diagrams updated with implementation
- Use diagrams for developer onboarding
- Document architectural decisions

### Maintenance Phase

- Regular diagram updates
- Version control diagram changes
- Use diagrams for impact analysis