What is layered?

Layered refers to a design approach where a system is divided into separate “layers,” each with its own responsibility. Think of a cake: each layer sits on top of the one below it, and you can work on one layer without messing up the others. In software, a layered architecture might have a presentation layer (what you see), a business logic layer (the rules), and a data layer (where information is stored). Each layer only talks to the layer directly beneath or above it, keeping things organized and easier to manage.

Let's break it down

  • Presentation Layer - Handles user interfaces, like web pages or mobile screens. It shows data and collects input.
  • Business Logic Layer - Contains the core rules and calculations of the application. It decides what to do with the data.
  • Data Access Layer - Communicates with databases or storage systems, reading and writing information.
  • Infrastructure Layer (optional) - Takes care of low‑level services such as logging, authentication, or networking. Each layer has a clear job, and they communicate through well‑defined interfaces, not by directly reaching into each other’s code.

Why does it matter?

  • Simplicity - Developers can focus on one piece at a time without worrying about the whole system.
  • Maintainability - Bugs or new features are easier to add because changes stay within a single layer.
  • Reusability - A business logic layer can be used by both a web app and a mobile app without rewriting code.
  • Scalability - You can upgrade or scale one layer (like moving the database to a bigger server) without touching the others.

Where is it used?

  • Web applications - Most modern sites separate the UI, server‑side logic, and database.
  • Mobile apps - The same pattern lets iOS and Android share core logic.
  • Enterprise software - Large business systems (ERP, CRM) rely on layered designs to manage complexity.
  • Operating systems - Even OS kernels often have hardware abstraction layers, driver layers, and user‑space layers.

Good things about it

  • Clear separation of concerns makes teamwork smoother; different developers can own different layers.
  • Testing becomes easier because you can test each layer in isolation.
  • Future upgrades are less risky; you can replace the presentation layer with a new UI without touching the data layer.
  • Encourages good coding practices like encapsulation and modularity.

Not-so-good things

  • Can introduce extra “overhead” because data must pass through multiple layers, potentially slowing performance.
  • May lead to over‑engineering for very small projects where a simple script would suffice.
  • If layers are not well defined, you might end up with “leaky abstractions” where one layer depends on the inner workings of another, defeating the purpose.
  • Requires disciplined documentation and communication; otherwise, the boundaries between layers can become blurry.