Domain-Driven Design Skill

Reference for domain modeling concepts from Eric Evans' "Domain-Driven Design: Tackling Complexity in the Heart of Software."

Activation Triggers

Use this skill when discussing:

• Domain modeling and ubiquitous language
• Bounded contexts and context mapping
• Entities vs value objects
• Aggregates and aggregate roots
• Repository and factory patterns
• Domain events and event storming
• Anti-corruption layers

Quick Reference

Strategic DDD Patterns

Tactical DDD Patterns

Building Blocks

Context Mapping Relationships

Aggregate Design Rules

1. Protect invariants - Aggregate root enforces all rules
2. Design for consistency - One aggregate per transaction
3. Reference by identity - Don't hold direct references to other aggregates
4. Use eventual consistency - Between aggregates, not within
5. Keep aggregates small - Focused on true invariants

Entity vs Value Object Decision

Does identity matter beyond its attributes?
├── YES → Entity (e.g., User, Order, Product)
└── NO → Value Object (e.g., Address, Money, DateRange)

Will instances be shared?
├── YES → Entity (needs identity for references)
└── NO → Value Object (can be replaced/copied)

Directory Structure

ddd/
├── SKILL.md
├── strategic/
│   ├── ubiquitous-language.md
│   ├── bounded-contexts.md
│   ├── context-mapping.md
│   └── anti-corruption-layer.md
├── tactical/
│   ├── entities.md
│   ├── value-objects.md
│   ├── aggregates.md
│   ├── domain-services.md
│   └── domain-events.md
├── patterns/
│   ├── repositories.md
│   ├── factories.md
│   └── specifications.md
└── practices/
    ├── event-storming.md
    └── model-exploration.md

Usage Examples

Modeling a Domain

Question: "How should I model orders?"

Consider:
1. Define Ubiquitous Language - See strategic/ubiquitous-language.md
2. Identify Entities vs Value Objects - See tactical/
3. Find Aggregates - See tactical/aggregates.md
4. Design Repositories - See patterns/repositories.md

Integrating Systems

Question: "How do I integrate with legacy system?"

Consider:
- Define Bounded Context boundary
- Use Anti-Corruption Layer
- Map contexts with Context Map

Based on concepts from "Domain-Driven Design" by Eric Evans.