This document was generated using AI and has yet to be human reviewed
Architecture Documentation
Implementation Layer — Mapping specification requirements to system structure
Definition
Architecture documentation describes the high-level structure of a system: its major components, how they interact, the boundaries between them, and the rationale for design decisions. It bridges the gap between abstract specification requirements and concrete implementation.
Relationship to the Specification
The specification defines what the system must do. Architecture documentation explains how the system is organized to fulfill those requirements.
Every architectural decision should trace back to one or more specification requirements:
| Specification Requirement | Architectural Response |
|---|---|
| ”Messages shall be delivered within 500ms” | Event-driven architecture with async message queues |
| ”Data shall be encrypted at rest” | Storage layer with transparent encryption |
| ”System shall support 10,000 concurrent users” | Horizontal scaling with load balancing |
| ”Components shall be independently deployable” | Microservices with defined service boundaries |
Core Components
- Component Diagrams: Visual representation of major system parts and their relationships
- Data Flow: How information moves through the system
- Integration Points: Where the system connects with external services or protocols
- Deployment Topology: How components map to infrastructure
- Design Rationale: Why specific approaches were chosen over alternatives
- Constraints & Trade-offs: Limitations accepted to meet requirements
Dependency Chain
Specification
↓
Architecture Docs ← translates requirements into structure
↓
Code & Comments ← implements the architecture
↓
Protocol Docs ← details inter-component communication
Why Spec-Grounding Matters
Architecture divorced from specification becomes arbitrary. Without clear traceability:
- Over-engineering: Components are built for imagined requirements rather than specified ones
- Under-engineering: Critical requirements are missed because they weren’t systematically traced
- Undefendable decisions: When challenged, architects can’t explain why the system is structured as it is
- Drift: As implementations evolve, the architecture no longer reflects either the spec or reality
Traceability Patterns
Good architecture documentation maintains explicit links to specification requirements:
## Message Routing Component
### Purpose
Implements requirements SPEC-4.2.1 through SPEC-4.2.7 (Message Delivery).
### Design Decisions
- **Async queue pattern**: Required by SPEC-4.2.3 (500ms delivery SLA)
- **At-least-once semantics**: Required by SPEC-4.2.5 (delivery guarantee)
- **Dead letter queue**: Required by SPEC-4.2.7 (failure handling)
Best Practices
- Create a requirements traceability matrix linking spec sections to architectural components
- Document decisions that extend beyond spec requirements separately from those that fulfill them
- Update architecture docs when specifications change—they should evolve together
- Include “out of scope” sections to clarify what the architecture intentionally does not address