# Domain Driven Design

> Domain-Driven Design reference for strategic and tactical modeling. Use when user says "model this domain", "design a bounded context", "create an aggregate", "what's a value object", "apply DDD", or asks about ubiquitous language, context mapping, entities, repositories, domain events, or aggregates. Do NOT use for infrastructure/DevOps, pure UI components, or simple CRUD without business rules.

- Skill: `bikach/domain-driven-design` (Agent Skill, multi-file: 13 files)
- Install (CLI): `npx skillmds@latest add bikach/domain-driven-design`
- Raw SKILL.md: https://api.skillmd.com/api/skills/bikach/domain-driven-design/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: Bikach (https://skillmd.com/u/bikach)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/bikach/domain-driven-design

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# Domain-Driven Design

Reference for applying Domain-Driven Design, split into **strategic** design (high-level
domain decomposition) and **tactical** design (building blocks inside a bounded context).

This skill uses progressive disclosure: read the relevant pattern file on demand instead
of loading everything at once.

## When to Use This Skill

- Modeling a new domain or refactoring an existing one
- Deciding where boundaries belong (bounded contexts, subdomains)
- Choosing the right tactical building block (entity vs value object vs aggregate)
- Establishing a shared vocabulary with the business (ubiquitous language)
- Designing repositories, domain events, factories, or domain services

Do NOT use for infrastructure/DevOps tasks, pure UI work, or anemic CRUD with no
business invariants.

## Workflow

1. **Start strategic.** Clarify the domain, subdomains, and bounded contexts before
   writing any code. Establish the ubiquitous language first.
2. **Map relationships** between contexts (partnership, conformist, anti-corruption layer, ...).
3. **Then go tactical** inside a single bounded context: model aggregates, entities,
   value objects, and the rules that protect invariants.
4. **Keep the language consistent** between code and the strategic model at all times.

## Strategic Design

High-level decomposition of the problem space.

| Pattern | File | Use for |
|---|---|---|
| Ubiquitous Language | [strategic/ubiquitous-language.md](strategic/ubiquitous-language.md) | Shared vocabulary between business and code |
| Subdomain Classification | [strategic/subdomain-classification.md](strategic/subdomain-classification.md) | Core / supporting / generic subdomains |
| Bounded Context | [strategic/bounded-context.md](strategic/bounded-context.md) | Defining explicit model boundaries |
| Context Mapping | [strategic/context-mapping.md](strategic/context-mapping.md) | Relationships & integration between contexts |

## Tactical Design

Building blocks inside a bounded context.

| Pattern | File | Use for |
|---|---|---|
| Entity | [tactical/entity.md](tactical/entity.md) | Objects with identity and lifecycle |
| Value Object | [tactical/value-object.md](tactical/value-object.md) | Immutable, identity-less concepts |
| Aggregate | [tactical/aggregate.md](tactical/aggregate.md) | Consistency boundaries & invariants |
| Domain Event | [tactical/domain-event.md](tactical/domain-event.md) | Something meaningful that happened |
| Repository | [tactical/repository.md](tactical/repository.md) | Persistence abstraction for aggregates |
| Factory | [tactical/factory.md](tactical/factory.md) | Complex object/aggregate creation |
| Domain Service | [tactical/domain-service.md](tactical/domain-service.md) | Stateless domain logic spanning entities |
| Specification | [tactical/specification.md](tactical/specification.md) | Reusable business rule / query predicate |

## Related Skills

- [[architecting-backend]] — hexagonal architecture, SOLID, where DDD building blocks fit
- [[security-guardian]] — validating invariants and inputs at domain boundaries