Subdomain Identification & Bounded Context Analysis

This skill analyzes codebases to identify subdomains (Core, Supporting, Generic) and suggest bounded contexts following Domain-Driven Design Strategic Design principles.

When to Use

Apply this skill when:

• Analyzing domain boundaries in any codebase
• Identifying Core, Supporting, and Generic subdomains
• Mapping bounded contexts from problem space to solution space
• Assessing domain cohesion and detecting coupling issues
• Planning domain-driven refactoring
• Understanding business capabilities in code

Core Principles

Subdomain Classification

Core Domain: Competitive advantage, highest business value, requires best developers

• Indicators: Complex business logic, frequent changes, domain experts needed

Supporting Subdomain: Essential but not differentiating, business-specific

• Indicators: Supports Core Domain, moderate complexity, business-specific rules

Generic Subdomain: Common functionality, could be outsourced

• Indicators: Well-understood problem, low differentiation, standard functionality

Bounded Context

An explicit linguistic boundary where domain terms have specific, unambiguous meanings.

• Primary nature: Linguistic boundary, not technical
• Key rule: Inside boundary, all Ubiquitous Language terms are unambiguous
• Goal: Align 1 subdomain to 1 bounded context (ideal)

Analysis Process

Phase 1: Extract Concepts

Scan codebase for business concepts (not infrastructure):

1. Entities (domain models with identity)

• Patterns: @Entity, class, domain models
• Focus: Business concepts, not technical classes

1. Services (business operations)

• Patterns: *Service, *Manager, *Handler
• Focus: Business logic, not technical utilities

1. Use Cases (business workflows)

• Patterns: *UseCase, *Command, *Handler
• Focus: Business processes, not CRUD

1. Controllers/Resolvers (entry points)

• Patterns: *Controller, *Resolver, API endpoints
• Focus: Business capabilities, not technical routes

Phase 2: Group by Ubiquitous Language

For each concept, determine:

Primary Language Context

• What business vocabulary does this belong to?
• Examples:
• Subscription, Invoice, Payment → Billing language
• Movie, Video, Episode → Content language
• User, Authentication → Identity language

Linguistic Boundaries

• Where do term meanings change?
• Same term, different meaning = different bounded context
• Example: "Customer" in Sales vs "Customer" in Support

Concept Relationships

• Which concepts naturally belong together?
• Which share business vocabulary?
• Which reference each other?

Phase 3: Identify Subdomains

A subdomain has:

• Distinct business capability
• Independent business value
• Unique vocabulary
• Multiple related entities working together
• Cohesive set of business operations

Common Domain Patterns:

• Billing/Subscription: Payments, invoices, plans
• Content/Catalog: Media, products, inventory
• Identity/Access: Users, authentication, authorization
• Analytics: Metrics, dashboards, insights
• Notifications: Messages, alerts, communications

Classify Each Subdomain:

Use this decision tree:

Is it a competitive advantage?
  YES → Core Domain
  NO → Does it require business-specific knowledge?
        YES → Supporting Subdomain
        NO → Generic Subdomain

Phase 4: Assess Cohesion

High Cohesion Indicators ✅

• Concepts share Ubiquitous Language
• Concepts frequently used together
• Direct business relationships
• Changes to one affect others in group
• Solve same business problem

Low Cohesion Indicators ❌

• Different business vocabularies mixed
• Concepts rarely used together
• No direct business relationship
• Changes don't affect others
• Solve different business problems

Cohesion Score Formula:

Score = (
  Linguistic Cohesion (0-3) +    // Shared vocabulary
  Usage Cohesion (0-3) +         // Used together
  Data Cohesion (0-2) +          // Entity relationships
  Change Cohesion (0-2)          // Change together
) / 10

8-10: High Cohesion ✅
5-7:  Medium Cohesion ⚠️
0-4:  Low Cohesion ❌

Phase 5: Detect Low Cohesion Issues

Rule 1: Linguistic Mismatch

• Problem: Different business vocabularies mixed
• Example: User (identity) + Subscription (billing) in same service
• Action: Suggest separation into different bounded contexts

Rule 2: Cross-Domain Dependencies

• Problem: Tight coupling between domains
• Example: Service A directly instantiates entities from Domain B
• Action: Suggest interface-based integration

Rule 3: Mixed Responsibilities

• Problem: Single class handles multiple business concerns
• Example: Service handling both billing and content
• Action: Suggest splitting by subdomain

Rule 4: Generic in Core

• Problem: Generic functionality in core business logic
• Example: Email sending in billing service
• Action: Extract to Generic Subdomain

Rule 5: Unclear Boundaries

• Problem: Cannot determine which domain concept belongs to
• Example: Entity with relationships to multiple domains
• Action: Clarify boundaries, possibly split concept

Phase 6: Map Bounded Contexts

For each subdomain identified, suggest bounded context:

Bounded Context Characteristics:

• Name reflects Ubiquitous Language
• Contains complete domain model
• Has explicit integration points
• Clear linguistic boundary

Integration Patterns:

• Shared Kernel: Shared model between contexts (use sparingly)
• Customer/Supplier: Downstream depends on upstream
• Conformist: Downstream conforms to upstream
• Anti-corruption Layer: Translation layer between contexts
• Open Host Service: Published interface for integration
• Published Language: Well-documented integration protocol

Output Format

Domain Map

For each domain/subdomain:

markdown
## Domain: {Name}

**Type**: Core Domain | Supporting Subdomain | Generic Subdomain

**Ubiquitous Language**: {key business terms}

**Business Capability**: {what business problem it solves}

**Key Concepts**:

- {Concept} (Entity|Service|UseCase) - {brief description}

**Subdomains** (if applicable):

1. {Subdomain} (Core|Supporting|Generic)
   - Concepts: {list}
   - Cohesion: {score}/10
   - Dependencies: → {other domains}

**Suggested Bounded Context**: {Name}Context

- Linguistic boundary: {where terms have specific meaning}
- Integration: {how it should integrate with other contexts}

**Dependencies**:

- → {OtherDomain} via {interface/API}
- ← {OtherDomain} via {interface/API}

**Cohesion Score**: {score}/10

Cohesion Matrix

markdown
## Cross-Domain Cohesion

| Domain A | Domain B | Cohesion | Issue              | Recommendation          |
| -------- | -------- | -------- | ------------------ | ----------------------- |
| Billing  | Identity | 2/10     | ❌ Direct coupling | Use interface           |
| Content  | Billing  | 6/10     | ⚠️ Usage tracking  | Event-based integration |

Low Cohesion Report

markdown
## Issues Detected

### Priority: High

**Issue**: {description}

- **Location**: {file/class/method}
- **Problem**: {what's wrong}
- **Concepts**: {involved concepts}
- **Cohesion**: {score}/10
- **Recommendation**: {suggested fix}

### Priority: Medium

{similar format}

Bounded Context Map

markdown
## Suggested Bounded Contexts

### {ContextName}Context

**Contains Subdomains**:

- {Subdomain1} (Core)
- {Subdomain2} (Supporting)

**Ubiquitous Language**:

- Term: Definition in this context

**Integration Requirements**:

- Consumes from: {OtherContext} via {pattern}
- Publishes to: {OtherContext} via {pattern}

**Implementation Notes**:

- Separate persistence
- Independent deployment
- Explicit API boundaries

Best Practices

Do's ✅

• Focus on business language, not code structure
• Let Ubiquitous Language guide boundaries
• Measure cohesion objectively
• Identify clear integration points
• Classify every subdomain (Core/Supporting/Generic)
• Look for linguistic boundaries first

Don'ts ❌

• Don't group by technical layers
• Don't force single global model
• Don't ignore linguistic differences
• Don't couple domains directly
• Don't create contexts by architecture
• Don't eliminate all dependencies (some are necessary)

Analysis Checklist

For Each Concept:

• ] What business language does it belong to?
• ] What domain/subdomain is it part of?
• ] Is it Core, Supporting, or Generic?
• ] What other concepts does it relate to?
• ] Are dependencies within same domain?
• ] Any linguistic mismatches?

For Each Domain:

• ] What is the Ubiquitous Language?
• ] What are the key concepts?
• ] What are the subdomains?
• ] Which is the Core Domain?
• ] What are cross-domain dependencies?
• ] Is internal cohesion high?
• ] Are boundaries clear?

For Cohesion Analysis:

• ] Calculate cohesion scores
• ] Identify low cohesion areas
• ] Map cross-domain dependencies
• ] Flag linguistic mismatches
• ] Note tight coupling
• ] Suggest boundary clarifications

Quick Reference

Subdomain Decision Tree

Analyze business capability
└─ Is it competitive advantage?
   ├─ YES → Core Domain
   └─ NO → Is it business-specific?
      ├─ YES → Supporting Subdomain
      └─ NO → Generic Subdomain

Cohesion Quick Check

Same vocabulary? → High linguistic cohesion
Used together? → High usage cohesion
Direct relationships? → High data cohesion
Change together? → High change cohesion

All high → Strong subdomain candidate
Mix of high/low → Review boundaries
All low → Likely wrong grouping

Bounded Context Signals

Clear boundary signs:
✅ Distinct Ubiquitous Language
✅ Concepts have unambiguous meaning
✅ Different meanings across contexts
✅ Clear integration points

Unclear boundary signs:
❌ Same terms with same meanings everywhere
❌ Concepts used identically across system
❌ No clear linguistic differences
❌ Tight coupling everywhere

Anti-Patterns to Avoid

Big Ball of Mud

• Everything connected to everything
• No clear boundaries
• Mixed vocabularies
• Prevention: Explicit bounded contexts

All-Inclusive Model

• Single model for entire business
• Impossible global definitions
• Creates conflicts
• Prevention: Embrace multiple contexts

Mixed Linguistic Concepts

• Different vocabularies in same context
• Example: User/Permission with Forum/Post
• Prevention: Keep linguistic associations

Notes

• This is strategic analysis, not tactical implementation
• Focus on WHAT domains exist, not HOW to implement
• Some cross-domain dependencies are normal
• Low cohesion doesn't always mean "bad," it means "needs attention"
• Generic Subdomains naturally have lower cohesion
• Always validate with domain experts when possible

Validation Criteria

Good domain identification has:

• ✅ Clear boundaries with distinct Ubiquitous Language
• ✅ High internal cohesion within domains
• ✅ Explicit cross-domain dependencies
• ✅ Business alignment with capabilities
• ✅ Actionable recommendations for issues