One Concern Per File

Kind: principle

Layer: Structural Core

Record: architecture:one-concern-per-file

Severity: mandatory

Scope: file

Canonical: Ontology

A design rule that each file plays exactly one declared role, and a file that plays two is split.

Listed in Architecture principles, after Sideways Overflow and before Narrowest Concern.

Requires

• Classification Judgment

Reinforces

• Separation of Concerns

Enables

• Narrowest Concern

Conflicts with

• Multi-Role File
• Sentence-Shaped Name

Violated by

• Multi-Role File

Refactored by

• Split by Responsibility

Severity

• mandatory

Category

• Taxonomy / Classification / Naming

Required by

• Collision Consolidation

Linked from

• Placement is a grammar
• The layer spine
• Core Modular Design
• Taxonomy / Classification / Naming
• Taxonomy / Classification / Naming
• Severity levels