Clean architecture

Why: the goal or problem

Readers save budget guides from web and CLI. Screen or database changes must spare the saving rule; use cases cannot import either.

How: work toward a solution

Fictional single process: Hana, Budget Guide unsaved. HTTP/CLI controller maps IDs into SaveArticle; SavedArticle validates them.
SaveArticle calls SaveRepository, implemented by memory/embedded-database adapters. Imports point inward: adapters → use-case contracts → domain; calls reach outward to storage. Only plain data crosses; ORM rows stay outside.
Saved: 0 → 1 entries; repeat → 1. Empty IDs or failure before writing → 0; retry after correction.

Dependency direction is not call direction

Illustrative example

Dependencies point toward policy

Hana wants to save the Budget Guide · initially unsaved

One process · dotted enclosure

1 · Frameworks & drivers

HTTP / CLI · Memory / Embedded database

↓ Source dependency

2 · Adapters

Controllers map IDs; storage adapters map records

↓ Source dependency

3 · Application policy

SaveArticle

Owns the SaveRepository interface

↓ Source dependency

4 · Domain policy

SavedArticle

Rejects empty reader/article IDs

At the storage boundary

← Source dependencySaveRepository (inside) ← storage adapter

Runtime call →SaveArticle → via SaveRepository → storage adapter (outside)

Plain IDs and Saved results cross the boundary; ORM rows stay outside. Four bands explain this example, not a required folder structure.

Save → repeat: 0 → 1 → 1 entries; return Saved.
From empty: empty IDs or failure before writing → 0. Retry after correction.

HTTP / CLI and memory / embedded database are alternatives; no data migration is implied.

The four policy bands share one process here. Inward source dependencies do not create independent deployment or failure isolation.

What: the concept

Clean architecture directs source dependencies toward policy. Runtime calls can travel outward through inward-owned interfaces. Martin

Mapping costs maintenance. Combine with hexagonal ports. Four folders are not mandatory.

Go further

Optional reading · separate from the overview

Selection & comparison

Choose inward policy dependencies when business rules must survive UI and database changes. Simple layers can suffice for stable roles; hexagonal ports emphasize the inside/outside interaction boundary. These views can describe the same system at different levels.

Applications

The budget guide maps HTTP or CLI input into SaveArticle and keeps database rows outside the policy. The example separates the caller’s runtime path from what each source module imports. Saving twice still has one record because the application defines that identity.

Implementation & cautions

Own the storage interface on the inner side, implement it outside, and inject an adapter at composition time. A runtime call may reach outward while its source dependency points inward. Mapping and tests cost maintenance; neither circular artwork nor folder names enforce the rule.

Evidence

Robert C. Martin: The Clean Architecture ↗
Original description of inward source dependencies and boundary data; concentric circles do not require four folders.
Checked 2026-09-27

Comparison within this category
Concept	Features	Advantages	Limitations	Suitable situations	Combination conditions
Clean architecture	Source dependencies point inward	Policy stays independent of framework data	Boundary mapping adds maintenance	Policy must outlive UI and database choices	Can use hexagonal ports at the edges

Comparison within this category

Concept

Features

Advantages

Limitations

Suitable situations

Combination conditions

Clean architecture

Source dependencies point inward

Policy stays independent of framework data

Boundary mapping adds maintenance

Policy must outlive UI and database choices

Can use hexagonal ports at the edges

Clean architecture

Why: the goal or problem

How: work toward a solution

Dependencies point toward policy

1 · Frameworks & drivers

2 · Adapters

3 · Application policy

4 · Domain policy

At the storage boundary

What: the concept

Go further

Apply this to your project

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