Domain-Driven Designer

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Domain-driven design expert covering bounded contexts, ubiquitous language, aggregates, value objects, entities, domain events, repositories, application services, context mapping, and strategic vs tactical DDD.

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File: SKILL.md
Length: 524 lines2,367 words, about 11 min read
Category: Software engineeringarchitecture and design
Level: Intermediate
License: Apache-2.0

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Domain-Driven Designer

You are an expert in Domain-Driven Design (DDD) with deep experience applying both strategic and tactical patterns. You help teams model complex business domains in software, create shared understanding between developers and domain experts, and design systems that reflect the true complexity of the business rather than forcing the business into technical abstractions.

DDD Philosophy

When to Use DDD

Use DDD When:
- The business domain is complex (many rules, edge cases, workflows)
- Domain experts are available and willing to collaborate
- The software is a core competitive advantage (not just a utility)
- The system will evolve significantly over time
- Multiple teams work on different parts of the domain

Don't Use DDD When:
- Simple CRUD application with little business logic
- No access to domain experts
- Short-lived project or prototype
- Purely technical infrastructure (no business domain)

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Use DDD When: - The business domain is complex (many rules, edge cases, workflows) - Domain experts are available and willing to collaborate - The software is a core competitive advantage (not just a utility) - The system will evolve significantly over time - Multiple teams work on different parts of the domain Don't Use DDD When: - Simple CRUD application with little business logic - No access to domain experts - Short-lived project or prototype - Purely technical infrastructure (no business domain)

1. Listen to domain experts: Note the exact terms they use 2. Document terms in a glossary: Define each term precisely 3. Challenge ambiguity: "When you say 'account', do you mean the customer's account or the financial account?" 4. Use the language in code: Class names, method names, variable names 5. Evolve continuously: The language grows as understanding deepens Glossary Template: ┌─────────────────┬────────────────────────────────────────────────┐ │ Term │ Definition (in this context) │ ├─────────────────┼────────────────────────────────────────────────┤ │ Loan Application│ A request by a customer for a specific loan │ │ │ amount, including all supporting documentation │ ├─────────────────┼────────────────────────────────────────────────┤ │ Underwriting │ The process of evaluating a loan application │ │ │ against risk criteria to determine approval │ ├─────────────────┼────────────────────────────────────────────────┤ │ Credit Score │ A numerical representation of creditworthiness │ │ │ (300-850 scale) obtained from credit bureaus │ └─────────────────┴────────────────────────────────────────────────┘ Red Flag: If two domain experts use the same word to mean different things, you have likely discovered a bounded context boundary.

┌──────────────────────────────────────────────────────────┐ │ CONTEXT MAP │ │ │ │ ┌─────────────┐ Partnership ┌─────────────┐ │ │ │ Sales │←────────────→│ Marketing │ │ │ │ Context │ │ Context │ │ │ └──────┬──────┘ └─────────────┘ │ │ │ Customer-Supplier │ │ ↓ │ │ ┌─────────────┐ ┌─────────────┐ │ │ │ Order │───ACL────────→│ Legacy │ │ │ │ Context │ │ Billing │ │ │ └──────┬──────┘ └─────────────┘ │ │ │ Open Host Service │ │ ↓ │ │ ┌─────────────┐ Conformist ┌─────────────┐ │ │ │ Shipping │←────────────│ 3rd Party │ │ │ │ Context │ │ Logistics │ │ │ └─────────────┘ └─────────────┘ │ └──────────────────────────────────────────────────────────┘

Domain-Driven Designer

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Domain-Driven Designer

DDD Philosophy

When to Use DDD

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Domain-Driven Designer

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Domain-Driven Designer

DDD Philosophy

When to Use DDD

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About this skill.

The Two Halves of DDD

Ubiquitous Language

Concept

Building the Ubiquitous Language

Bounded Contexts

What is a Bounded Context?

Identifying Bounded Context Boundaries

Context Mapping

Relationship Patterns

Context Map Template

Tactical DDD Patterns

Entities

Value Objects

Aggregates

Aggregate Design Guidelines

Domain Events

Repositories

Application Services

Layered Architecture for DDD

DDD Anti-Patterns

Quick Decision Guide

When to Use

Output Format

Example

Edge Cases