Every system contains two kinds of code: one that defines what the business does, and one that just makes it run.

The first is the core — the rules, decisions, and logic that give the system purpose. The second is replaceable — the frameworks, databases, and interfaces that move data around.

Good architecture makes this boundary unmistakable and guards the core from the churn outside it.

Business Rules Are the Heart of the System

The domain logic is where value lives. It encodes how the business thinks — how things are priced, approved, shipped, or rejected. Frameworks, databases, APIs, and UIs are just the delivery channels. They carry the logic, not define it.

When these layers get tangled, the system starts serving the tools instead of the business.

Keep the core pure: rules define behavior; tools execute it. The more your domain can run without knowing how it’s deployed, the more stable your system becomes.

Frameworks Are Disposable

Frameworks exist to handle infrastructure — routing, persistence, messaging, I/O. They solve the same problem every system faces: moving bits in and out. They are scaffolding, not structure.

Wrap them behind clear boundaries. That way, when a new framework or database replaces the old, the business logic remains untouched.

Durability in architecture isn’t about never changing tools — it’s about being able to change them without rewriting the system’s brain.

Structure Should Express Intent, Not Technology

A codebase should read like a map of the business, not a catalog of frameworks. If the first things you see are controllers/, repositories/, and services/, you’re reading implementation, not intent.

The structure should expose the domain’s language, like orders/, billing/, inventory/. When your directories mirror real-world capabilities instead of technical layers, the system tells you what it does at a glance. Architecture becomes documentation.

Conclusion

Protect the part of the system that changes slowest: the business rules. Everything else — frameworks, storage, APIs, delivery layers — is just replaceable machinery.

When your architecture reflects the business, not the tools, change becomes controlled and reversible. The core stays stable, even as the world around it shifts.

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