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Software Engineering Principles

Software engineering is a complex discipline that requires specific knowledge and skill. But there are a number of tried-and-true principles that can help engineers build better and more reliable software applications.

One such principle is the KISS principle, which urges developers to keep their code simple. This can help reduce bugs and make it easier for others to understand and modify.

Open/Closed Principle (OCP)

The O in the SOLID principle stands for “Open/Closed.” This principle states that classes should be open to extension but closed to modification. This is a common software engineering principle that helps developers keep their code flexible and maintainable.

This principle requires that you use polymorphism to extend the behavior of a class, instead of directly changing its source code. It also means that you should avoid using multiple if-else statements and switch cases, since these can violate this principle.

While this doesn’t mean that a class cannot be modified (bug fixes are fine) it should be done by creating a new class that inherits from the original. This will allow you to add functionality without breaking the existing code base.

Liskov Substitution Principle (LSP)

The Liskov Substitution Principle (LSP) is a related software engineering principle to Single Responsibility Principle (SRP). It states that a child class should be able to replace its parent class without introducing unexpected behavior.

This mainly applies to inheritance hierarchies but can also be applied to interfaces and abstract classes. LSP helps ensure that derived types follow SRP and don’t introduce unrelated responsibilities.

To comply with LSP, a child class should have a valid implementation of all methods of its supertype. The implementation of these methods should also satisfy all pre-conditions and post-conditions defined in the supertype’s invariants. This will prevent the program from breaking at runtime if the child class is substituted for its supertype.

Interface Segregation Principle (ISP)

The fourth principle of SOLID is the Interface Segregation Principle (ISP). This principle states that a client should not be forced to depend on methods it does not use. This principle encourages the design of small, client-specific interfaces.

In addition, it reduces coupling by separating methods that are not used by clients. It also helps improve modularity and flexibility by making it easier to add and change functionality.

However, it is important to apply this principle with caution. It can be easy to overuse it and end up with a lot of interfaces that contain only one method each. This can cause a large amount of code to be unused and is not conducive to good programming practices.

Dependency Inversion Principle (DIP)

The Dependency Inversion Principle (DIP) encourages software architects to separate higher-level modules from lower-level modules. This makes the code more flexible and easier to maintain.

High-level modules like the Policy Layer or Mechanism Layer should not depend directly on low-level modules. Instead, they should depend on abstractions, like interfaces.

This decouples the higher-level classes from the lower-level implementation and allows them to be replaced or tested independently. It also makes the code more flexible and easier to test. Many popular frameworks, such as Spring and Angular, follow this principle. This is a key part of the Inversion of Control pattern and Dependency Injection.


As a software engineering principle, PoLA emphasizes that user interfaces and other components should match expectations users have about how they should behave. This minimizes surprises for both users and other developers interacting with the component and makes the interface easier to understand and maintain.

Document your design principles in an accessible place, such as a shared wiki or intranet. This ensures that your team can access them whenever they need to and fosters a culture of understanding and adherence to these best practices.

Present the principles in a series of workshops or tutorials to familiarize your team with them. Then, incorporate them into your onboarding and training programs to reinforce their importance.


The YAGNI principle (“You Ain’t Gonna Need It”) is a software engineering principle that suggests developers shouldn’t create features that are not necessary. This is a key element of agile development, and it helps prevent code bloat and technical debt.

It’s easy for engineers to fall into the trap of over-engineering. They may feel tempted to add a feature because it solves a problem they had in the past or because they’re convinced that it will be useful in the future.

This is where the Open/Closed Principle comes in, which encourages reusable modules and modularity, so they can be easily extended or modified. When combined with YAGNI, this allows teams to avoid unnecessary complexity and improve product clarity.

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