What Are Software Design Principles?

Software design principles are general guidelines and best practices that are used to create software that is maintainable, scalable, and efficient. These principles are intended to guide the process of designing software and help ensure that it is well-structured, easy to understand, and easy to modify, reducing the likelihood of bugs and improving the overall quality of the software.

This is part of a series of articles about system design.

In this article:

  • Why Are Software Architecture Design Principles Important?
  • Best Software Design Principles for Successful Engineering
    • SOLID Principles
    • Don’t Repeat Yourself (DRY)
    • Encapsulation Principle
    • Principle of Least Astonishment (PoLA)
    • You Aren’t Gonna Need It (YAGNI)
    • Keep It Simple, Stupid (KISS)
    • Sharing Design Principles Effectively

Why Are Software Architecture Design Principles Important?

Software architecture design principles are important for several reasons:

  • Maintainability: By adhering to design principles, developers can create software that is easier to maintain, modify, and troubleshoot. This reduces the time and effort required for bug fixes, updates, and enhancements.
  • Scalability: Good architecture design ensures that software can accommodate growth and increased demand without significant rework or performance degradation. This allows the software to serve more users and handle more data efficiently.
  • Reusability: Design principles encourage the creation of modular and reusable components. This promotes efficiency by allowing developers to leverage existing code, reducing the need to write redundant or duplicate functionality.
  • Flexibility: A well-designed software architecture allows for easy adaptation to changing requirements, technologies, or business needs. This enables developers to quickly respond to market changes and stay competitive.
  • Readability: By following design principles, code is more organized, coherent, and easier to understand. This not only benefits the original developers but also makes it easier for new team members to contribute to the project.
  • Collaboration: A well-structured software architecture facilitates teamwork by providing clear boundaries and responsibilities for different components. This promotes parallel work and efficient communication among team members.
  • Quality: Adhering to software architecture design principles often results in higher-quality software that is more reliable, secure, and performant. This ultimately leads to better user experiences and higher customer satisfaction.
  • Cost reduction: By following design principles, developers can avoid many common pitfalls and mistakes that lead to costly rework, delays, or failures. This ultimately saves time and resources, resulting in a more cost-effective development process.

6 Software Design Principles for Successful Engineering

We cherry-picked the most widely agreed upon design principles from the software engineering community. Of course, each organization or codebase might have their own unique circumstances, so some might not be applicable to your exact situation. But if you adapt these principles to your own project, you will most likely be on the right track.

1. SOLID Principles

The SOLID principles are a set of software design guidelines that help developers create more maintainable, flexible, and robust software systems. Here is an explanation of each principle:

Single Responsibility Principle (SRP)

This principle states that each class or module should have only one reason to change, meaning it should have a single responsibility or purpose. By adhering to SRP, developers can create a more modular and maintainable codebase, as changes to one functionality do not affect unrelated parts of the system. A microservices architecture usually relies on this principle to ensure that each service has a single purpose, commonly in the repository level. See our post on microservices.

Open/Closed Principle (OCP)

According to OCP, software entities (classes, modules, functions, etc.) should be open for extension but closed for modification. In other words, developers should be able to add new features or functionality to an existing entity without changing its existing code. This is typically achieved through inheritance or composition, which allows for a more stable and less error-prone codebase.

Liskov Substitution Principle (LSP)

LSP states that objects of a derived class should be able to replace objects of the base class without affecting the correctness of the program. This means that derived classes must honor the contracts, behavior, and properties of the base class, ensuring that the software remains consistent and reliable also when new subclasses are introduced.

Interface Segregation Principle (ISP)

ISP emphasizes that clients should not be forced to depend on interfaces they do not use. Instead, interfaces should be segregated into smaller, more specific ones, allowing clients to depend only on the relevant interfaces. This reduces the coupling between components and improves the maintainability and flexibility of the software.

Dependency Inversion Principle (DIP)

DIP advocates for the inversion of dependencies between high-level and low-level modules. High-level modules should not depend on low-level modules directly. Instead, both should depend on abstractions. For example, if a high level module requires a logging capability, it should not directly reference a low-level logging library. Instead, it should reference an abstracted logging service, making it possible to switch out the logging library in the future.

This principle allows for greater flexibility and easier adaptation to changes, as high-level modules can be easily switched to work with different low-level implementations without needing modification.

2. Don’t Repeat Yourself (DRY)

The DRY principle emphasizes the importance of avoiding duplication in code. Duplication can lead to inconsistencies, increased maintenance effort, and a higher likelihood of introducing errors when changes are required.

To adhere to the DRY principle, developers should utilize abstractions, modularization, and reusable components to eliminate redundancy, ensuring that each piece of functionality is implemented in only one place. A simple example would be to create a function and call it from multiple locations, rather than implementing the same functionality multiple times.

3. Encapsulation Principle

Encapsulation is a core concept in object-oriented programming that promotes the bundling of data (attributes) and methods (functions) that operate on the data within a single unit, typically a class.

This principle advocates for hiding the internal workings of a class and exposing only what is necessary through a well-defined interface. By doing so, developers can prevent unintended access or modification of internal data, reduce coupling between components, and simplify the maintenance and modification of the code.

This principle is not limited to object-oriented programing, can also be applied to data structures, file formats or network traffic.

4. Principle of Least Astonishment (PoLA)

PoLA is a design guideline that encourages developers to create software components that behave predictably and intuitively, minimizing surprises for users or other developers interacting with the component.

This principle applies to user interfaces, APIs, and code. By adhering to PoLA, developers create software that is easier to use, understand, and maintain, ultimately reducing the likelihood of errors and misunderstandings.

5. You Aren’t Gonna Need It (YAGNI)

YAGNI is a principle that advises against implementing features or functionality before they are actually needed. This approach encourages developers to focus on the current requirements and avoid over-engineering, which can lead to increased complexity, longer development time, and wasted effort.

6. Keep It Simple, Stupid (KISS)

The KISS principle emphasizes the importance of simplicity in software design. It encourages developers to avoid unnecessary complexity and create straightforward, easy-to-understand solutions.

By keeping the design simple, developers can reduce the chances of introducing errors, improve maintainability, and make it easier for others to understand and contribute to the codebase. KISS does not mean oversimplifying or ignoring essential requirements; instead, it suggests finding the simplest solution that meets the project's needs.

Sharing Design Principles Effectively

Sharing design principles effectively is crucial for creating a consistent understanding and approach to software development within a team or organization. Here are some strategies to communicate design principles effectively:

  • Documentation: Clearly document your design principles in an accessible format, such as a shared wiki or internal website. Provide concise explanations, examples, and use cases to illustrate each principle in a meaningful way. Keep the documentation up-to-date and easy to navigate.
  • Training: Incorporate design principles into onboarding and training programs for new team members. Provide workshops, tutorials, or presentations to help developers understand and internalize the principles. Encourage experienced team members to share their knowledge and experiences.
  • Code reviews: Encourage the use of design principles during code reviews. Team members should actively discuss and evaluate the adherence to principles when reviewing code. This promotes awareness, encourages learning, and helps to reinforce the importance of following design principles.
  • Regular discussions: Hold regular meetings or discussions to review and assess the effectiveness of the design principles in practice. Identify areas where the principles are not being followed and address them through training or process improvements.
  • Real-world examples: Share examples of successful projects or case studies that demonstrate the benefits of adhering to design principles. This helps to illustrate their value and motivate team members to follow them in their work. If possible, it is better to show how the principles have been applied in your organization.
  • Leadership commitment: Ensure that leadership supports and promotes the use of design principles within the organization. This can help create a culture that values good software design and fosters a shared understanding of best practices.
  • Adapt and evolve: Regularly reevaluate and refine your design principles to ensure they remain relevant and effective. Solicit feedback from team members and incorporate lessons learned from past projects to improve and adapt the principles as needed.

Promoting Adoption of Design Principles with Swimm

One of the major challenges of adopting software design principles is communicating them, both when they are introduced for the first time and also for new contributors to the project.

With Swimm’s engineering knowledge management solution:

  • Engineers can effectively communicate the importance and practice of design principles in their software project.
  • Engineers can create rich documents with code examples, and automatically ensure they are up to date when the code changes.
  • A design pattern can be exemplified, using an example from your codebase. For the developers who will read a document about the principle, a real example is easy to relate to. It also provides a good basis when seeking to apply the design principle.

Moreover, creating a document with a real example is a much easier task than writing an abstract document. If an example already exists in your codebase, there's no need to invent a new one. All you have to do is describe it. It also helps you remember all the details, as you consider a concrete, real example from your code. Not all of the implementation details are important to mention or explain, yet it makes sure you don't forget about those that are.

With Swimm, such documents are maintainable. By code coupling to an existing example, if something ever changes in the system and the example changes, your document will be updated.

Swimm Playlists can be used to organize and reuse documentation, specifically for new contributors who join the codebase. You can embed documents describing the design patterns within the Playlists.

Learn more about Swimm