How to Divide a System into Clear Components Without Adding Complexity

Part Three of the Series: Building the Right Software Systems

"Every large software system started as a collection of small files. The difference between a system that succeeds and one that turns into chaos lies in how those files were organized from the beginning."

After understanding the problem in the previous article, we arrive at the next step—one of the most influential decisions in determining the lifespan of a software project: How should we divide the system?

At first glance, this may seem like a technical question, but in reality, it is an engineering decision. The way we structure a system today determines how easy it will be to develop after one year, after three years, and when the team grows to ten or twenty developers.

Many projects don't fail because the code is bad—they fail because they never established clear boundaries between the different parts of the system.

A System Is Not Just a Collection of Files

When a new project begins, everything seems simple.

We have:

• A Controllers folder
• A Services folder
• A Models folder
• A Repositories folder

As the project grows, problems begin to appear. Every service depends on five other services. Every controller knows database details. Every component can directly call every other component. Eventually, no one knows where a new feature actually belongs. The problem isn't the folder names. The problem is that the system no longer has clear boundaries.

Every Component Should Have One Responsibility

One of the fundamental principles of software design is that every component should have a clear reason for existing. Imagine we're building an order management system. We have several distinct responsibilities:

• Customer management
• Product management
• Order creation
• Payment processing
• Sending notifications
• Invoice generation

Each of these represents a separate responsibility. If we place all of them inside a single service called OrderService, it will eventually become a massive file with thousands of lines of code, making every modification risky. But when each responsibility is separated into its own component, the system becomes easier to understand and much safer to extend.

Boundaries Matter More Than Layers

Many developers spend a great deal of time organizing layers:

• Controller
• Service
• Repository

But they rarely ask a more important question: Where does this component's responsibility end, and where does another component's responsibility begin?

Consider creating a new order. Who should be responsible for:

• Verifying product availability?
• Calculating the final price?
• Applying discounts?
• Creating the invoice?
• Sending a confirmation message?

If these responsibilities are scattered randomly throughout the system, every new feature becomes difficult to implement. When the boundaries are clear, every component knows exactly what it should—and should not—do.

Don't Let Everything Know About Everything

One of the biggest causes of complexity is excessive coupling between components. It usually starts innocently. The Customer Service calls the Order Service. The Order Service calls the Payment Service. The Payment Service depends on the User Service. Then the Notification Service depends on all of them. Eventually, the system turns into a tightly connected web that cannot be separated. A small change in one place suddenly affects five others. Every new dependency increases the complexity of the system. Before making one component depend on another, ask yourself: Is this dependency really necessary?

Don't Design Around the Database

This is one of the most common design mistakes. The project begins with tables such as:

• Users
• Orders
• Products
• Payments

The tables become models. The models become the foundation of the entire system. But businesses don't operate around database tables. They operate around concepts such as:

• Customer
• Order
• Purchase
• Shipment
• Invoice

The database is simply a way to store those concepts. If it becomes the center of your design, it will limit the way you think. Start with the domain, then design the database to serve it—not the other way around.

Make the Project Easy to Read

Imagine a new developer joins your team. What's the first thing they'll do? They'll open the project and try to understand it. If it takes them only two hours to find where the Order feature lives, that's a good sign. If they have to search through dozens of folders and files, the problem isn't the new developer. The problem is the organization of the project. A well-designed system naturally guides developers to the right place.

Simplicity Is an Engineering Decision

Sometimes we assume that a professional system must contain dozens of layers, hundreds of interfaces, and design patterns everywhere. But every additional layer comes with a cost. Every unnecessary abstraction makes the system harder to understand.

Always ask yourself: Did I introduce this abstraction because the problem requires it, or because I saw it in another project? Good abstractions solve real problems. Premature abstractions create new ones.

How Do You Know the Design Is Good?

There is no single rule that fits every project. However, there are strong indicators:

• A feature can be modified without affecting the rest of the system.
• Every component has a clearly defined responsibility.
• There are no unnecessary dependencies between components.
• A new developer can easily locate any feature.
• You don't need to understand the entire project to modify one small part.

If these statements are true, you're moving in the right direction.

Common Mistakes

Some of the most common mistakes in software projects include:

• Creating massive services with dozens of responsibilities.
• Making every component depend on every other component.
• Organizing the project by file type instead of business domain.
• Adding unnecessary layers and abstractions.
• Placing business logic in inappropriate locations such as controllers or models.

These mistakes may not hurt during the first month. But they become extremely expensive once the project starts to grow.

Principles to Remember

Before adding any new component to your system, ask yourself:

• What is its single responsibility?
• Does it truly need to know about this other component?
• Can it be understood independently?
• Will it still be clear one year from now?
• Will it make the system simpler—or more complicated?

If the answers aren't clear, it's probably time to rethink the design.

Conclusion

Dividing a system is much more than organizing folders or choosing a particular architectural pattern. It is the process of giving every component clear boundaries, a well-defined responsibility, and enough independence to allow the system to evolve over time. The clearer those boundaries are, the easier the project becomes to understand, the faster it is to develop, and the less likely it is to suffer from unintended side effects.

In the next article, we'll discuss a topic that is often misunderstood at the beginning of software projects: When should you care about scalability, and when is it too early to think about it? We'll explore how to balance building a simple system today while preparing for tomorrow's growth—without falling into the trap of premature complexity.