How to Organize Modules in Software Architecture

In software engineering, while module dependencies ideally form a tree structure, real-world implementations often adopt Directed Acyclic Graphs (DAGs) to enable practical code reuse. This article explores three fundamental patterns of module organization and their implications.

Ideal Scenario: Hierarchical Tree Structure

Characteristics of Tree Architecture

Key Features:

• Unidirectional dependencies (parent → child)
• Clear hierarchical separation (e.g., UI → Business Logic → Data Layer)
• No circular references

Common Implementations:

• MVC Architecture
• Clean Architecture
• Three-Layer Pattern (Presentation/Logic/Data)

Advantages:
✅ Straightforward dependency management
✅ Explicit separation of concerns
✅ Simplified testing and maintenance

Challenges:
⚠️ Limited code reuse opportunities
⚠️ Potential for artificial module fragmentation
⚠️ Suboptimal for complex systems with cross-cutting concerns

Practical Reality: Directed Acyclic Graph (DAG)

Modern Dependency Management

Key Features:

• Shared modules between components (E shared by B/C)
• Multiple dependency paths
• Strictly acyclic

Real-World Applications:

• React/Vue Component Systems
• Webpack Module Federation
• Bazel Build System
• Database Schema Design

Advantages:
✅ Natural code reuse through shared modules
✅ Flexible architecture for complex systems
✅ Maintains dependency integrity

Implementation Considerations:
🔧 Requires robust tooling (TypeScript path resolution, Webpack aliases)
🔧 Needs dependency visualization tools
🔧 Demands strict code review practices

Anti-Pattern: Circular Dependencies

Dangerous Dependency Loops

Consequences:
❌ Runtime initialization errors (Cannot access 'X' before initialization)
❌ Compilation failures (ESM/TypeScript circular reference errors)
❌ Unmaintainable "spaghetti code" structure

Common Culprits:

• Bidirectional controller-service relationships
• Shared state management traps
• Improper dependency injection

Architectural Strategies

1. Dependency Hoisting

Elevate shared dependencies to higher-level modules to prevent duplication while maintaining acyclicity.

2. Dependency Injection

Implement IoC containers to manage cross-module dependencies:

// Angular-style DI example
@Injectable({ providedIn: 'root' })
export class SharedService {
  // Reusable business logic
}

3. Module Federation

Modern solutions for microfrontend architectures:

// Webpack Module Federation Configuration
new ModuleFederationPlugin({
  name: 'app1',
  exposes: {
    './Widget': './src/components/Widget',
  }
})

Industry Case Studies

Best Practices Checklist

1. Static Analysis

   • Enable TypeScript's --noImplicitCircularity
   • Use ESLint import/no-cycle rule

2. Dependency Visualization

   npx madge --image graph.svg src/index.ts
   

3. Architectural Guardrails

   • Enforce layer access rules in tsconfig.json
   • Implement module boundary checks in CI pipelines

4. Refactoring Techniques

   • Apply Dependency Inversion Principle (DIP)
   • Utilize facade patterns for cross-module communication

"Good architecture maximizes the number of decisions not made."
― Robert C. Martin (Clean Architecture)

By understanding these fundamental patterns and implementing appropriate guardrails, teams can create maintainable systems that balance architectural purity with practical reuse requirements.