# Architecture Paradigm Layered > Layered (n-tier) architecture with enforced layer boundaries and separation of concerns. Use when this capability is needed. - Skill: `tomevault-io/architecture-paradigm-layered` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/architecture-paradigm-layered` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/architecture-paradigm-layered/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/architecture-paradigm-layered --- ## Table of Contents - [When to Employ This Paradigm](#when-to-employ-this-paradigm) - [When NOT to Use This Paradigm](#when-not-to-use-this-paradigm) - [Adoption Steps](#adoption-steps) - [Key Deliverables](#key-deliverables) - [Technology Guidance](#technology-guidance) - [Risks & Mitigations](#risks-mitigations) - [Troubleshooting](#troubleshooting) # The Layered (N-Tier) Architecture Paradigm ## When to Employ This Paradigm - When teams need clear architectural boundaries and a familiar structure for moderate-sized systems. - When compliance or operations teams require clear separation of concerns (e.g., UI vs. domain logic vs. persistence). - When the deployment artifact remains a monolith, but code clarity and separation are degrading. ## When NOT To Use This Paradigm - When high scalability demands require independent scaling of components - When multiple teams need independent deployment cycles - When complex business logic requires frequent cross-layer communication - When microservices architecture is already planned or in place - When real-time processing requirements make layered communication too slow ## Adoption Steps 1. **Define the Layers**: Establish a clear set of layers. A common stack includes: Presentation -> Application/Service -> Domain -> Data Access. 2. **Enforce Dependency Direction**: Code in a given layer may only depend on the layer immediately below it. Forbid any "upward" dependencies or imports. 3. **Centralize Cross-Cutting Concerns**: Implement concerns like logging, authentication, and validation as centralized middleware or policies, rather than duplicating this logic in each layer. 4. **Test Each Layer Appropriately**: Apply testing strategies suitable for each layer, such as unit tests for the domain layer, service-layer tests for orchestration logic, and integration tests for persistence adapters. 5. **Document and Enforce Interactions**: Maintain up-to-date dependency diagrams and use automated architecture tests to prevent developers from creating "shortcut" dependencies that violate the layering rules. ## Key Deliverables - An Architecture Decision Record (ADR) that captures the responsibilities of each layer, the allowed dependencies between them, and the policy for any exceptions. - A formal dependency diagram stored with the project documentation. - Automated architectural checks (e.g., using ArchUnit, dep-cruise, or custom scripts) to prevent rule violations from being merged. ## Technology Guidance **Layer Implementation Patterns**: - **Presentation Layer**: React/Vue/Angular (Frontend), MVC Controllers (Backend) - **Application Layer**: Service classes, Application services, Use case orchestrators - **Domain Layer**: Business entities, Domain services, Business rules validation - **Data Access Layer**: Repository pattern, ORM mappers, Data access objects (DAO) **Architecture Enforcement Tools**: - **Java**: ArchUnit for dependency rule testing - **JavaScript/TypeScript**: ESLint rules with dependency tracking - **C#**: NDepend for architectural analysis - **Python**: Custom decorators and import analysis tools **Common Layer Stacks**: - **3-Layer**: Presentation → Business Logic → Data Access - **4-Layer**: Presentation → Application → Domain → Infrastructure - **5-Layer**: UI → Controller → Service → Domain → Persistence ## Real-World Examples **Enterprise ERP Systems**: SAP and Oracle ERP use layered architecture to separate user interfaces from business logic and database operations, enabling different frontend applications to share the same business rules. **Banking Applications**: Financial institutions employ layered architecture to maintain strict separation between customer-facing interfaces, transaction processing, and secure data storage for regulatory compliance. **E-commerce Platforms**: Traditional e-commerce sites use layered architecture to separate product catalogs, shopping cart logic, order processing, and payment handling into distinct layers. ## Risks & Mitigations - **Excessive Rigidity and Latency**: - **Mitigation**: For features that span multiple layers, strict adherence can lead to excessive "pass-through" code and increased latency. In such cases, consider using a Façade pattern to provide a more direct interface where appropriate. - **"Leaky" Layers**: - **Mitigation**: Developers may be tempted to bypass architectural rules for expediency, which degrades the architecture. Treat all architectural violations as build-breaking failures or critical issues in code review. ## Troubleshooting ### Common Issues **Command not found** Ensure all dependencies are installed and in PATH **Permission errors** Check file permissions and run with appropriate privileges **Unexpected behavior** Enable verbose logging with `--verbose` flag --- > Converted and distributed by [TomeVault](https://tomevault.io/claim/athola) — claim your Tome and manage your conversions.