Designing APIs and SDKs: A Look at Ousterhout’s Philosophy

Greetings developers! Today, we're diving into the fascinating world of Application Programming Interfaces (APIs) and Software Development Kits (SDKs). Designing these interfaces and kits is an art form in itself, an art form that leans heavily into the core principles of computer science and software design.

Earlier in my career, an old boss gifted me a book that has remained a valuable companion on my coding journey: "A Philosophy of Software Design" by John Ousterhout. The book, an insightful exploration of software design principles, emphasizes the importance of problem decomposition and understanding users. This philosophy has shaped my approach to API and SDK design and I believe it can be transformative for other developers too. He told me a story about how he read it on vacation (I was a little weirded out by this) and how it was literally his favourite book on software design. I went home and added it to my stack of CS books, but didn't get around to reading it until this little sabbatical I'm on. I'm really glad I did, what an eye-opener. I've been recommending it to everyone I know, and in an effort to solidify my own understanding of the concepts, I decided to write this!

Understanding Your Users

APIs and SDKs are indispensable tools in a developer's arsenal. APIs define how software applications interact, while SDKs provide a collection of tools and libraries that enable developers to create applications for specific platforms or frameworks.

However, to effectively design APIs and SDKs, one must deeply understand the users. After all, it's fellow developers who interact with your interfaces and kits, and their needs should spearhead your design process. You must grasp their technical capabilities (though it could be argued a great API is sufficiently simple enough that anyone could use it), their requirements, and the problems they're trying to solve. An excellent API or SDK should not only meet these needs but do so in a manner that's intuitive and efficient.

Central to this understanding is the concept of problem decomposition. In his book, Ousterhout emphasizes the significance of this concept, which involves breaking down large, intricate problems into smaller, more manageable sub-problems.

Decomposing Your Design

The concept of problem decomposition is a cornerstone of Ousterhout's philosophy and forms the bedrock of good API and SDK design. The process starts with a deep understanding of the users. Who are they? What are their needs? What problems are they trying to solve?

Once we have a grasp on these questions, we start to decompose the problem into key user functions, common tasks, and types of data interactions. This decomposition isn't arbitrary; it's based on a profound understanding of the user and their needs. By breaking down these functions into distinct modules, we're not just simplifying our API or SDK, but also making it easier to maintain and improve.

But problem decomposition doesn't end there. It's an ongoing process that requires constant re-evaluation and refinement. As the needs of the users evolve, so should our design. Our modules should be flexible enough to adapt to new user requirements or tasks.

Maintaining Consistency

With our design decomposed into manageable modules, we now shift our focus to consistency. Consistency is the thread that binds these separate modules together, forming a cohesive API or SDK. It is crucial in creating an interface that is predictable and reliable.

Uniform naming conventions, error handling, method usage, and response format ensure that our design is consistent. But it's not just about the outward appearance. The underlying code should also be consistent in its style and structure. This uniformity simplifies the development process and makes it easier for developers to understand and use our tools.

However, maintaining consistency is not a one-time task. As we add new modules or make changes to our design, we must ensure that these additions fit seamlessly into the existing structure. They should feel like a natural extension of the API or SDK, not an afterthought.

Keeping It Simple

Simplicity is a concept that's close to Ousterhout's heart. He states that “complexity is the worst enemy of software.” An API or SDK should be easy to use but powerful enough to accomplish complex tasks. This might seem like a paradox, but it's more of a balancing act.

Achieving this balance requires careful design. Each component of our API or SDK should be focused and efficient, handling a specific task or function. By doing so, we create a streamlined workflow that is intuitive to use. Developers should be able to easily figure out which component to use for a given task, without having to wade through unnecessary complexity.

However, simplicity should not come at the expense of functionality. Even as we strive to make our API or SDK simple and user-friendly, it should still be powerful and versatile enough to handle a wide range of tasks and scenarios.

Deep Modules

Deep modules are a hallmark of Ousterhout's philosophy. A deep module is one that provides a wide range of functionality while exposing a simple interface. This means that the module can handle complex tasks or operations, but its usage is straightforward and uncomplicated.

Creating deep modules requires thoughtful design. We need to consider not only what the module does, but also how it does it. The underlying code should be robust and efficient, capable of handling a variety of scenarios. At the same time, the interface should be clean and intuitive, making it easy for developers to use the module.

This balance between complexity and simplicity is what makes a module 'deep'. It's not about packing as much functionality as possible into a module, but rather about providing powerful functionality in a user-friendly package.

Deep Modules in Action

In the context of APIs and SDKs, deep modules play a crucial role. They enable the provision of rich, complex functionalities without overwhelming the developers with their complexity. They help in keeping the interfaces of the APIs or SDKs clean and easy to understand, while ensuring that these tools are powerful and versatile.

Deep modules also contribute to the maintainability and extensibility of APIs and SDKs. Their modular nature means that they can be updated or extended independently of each other, making it easier to keep the API or SDK up-to-date and relevant to evolving user needs.

In conclusion, creating deep modules is indeed a critical aspect of API and SDK design, embodying the essence of Ousterhout's philosophy. By striving to create deep modules, we can create APIs and SDKs that are not just powerful and robust, but also user-friendly and intuitive to use. As developers, that should be our ultimate goal.

Document Your Design, But Don't Overdo It

Ousterhout believes that "Complexity should be visible in the code, but not in the interfaces." This idea underscores the importance of good documentation. Comprehensive, clear documentation reveals the complexity of the code while keeping the interfaces clean and simple.

Good documentation goes beyond just explaining what each component does. It also provides examples of how to use the components, offers troubleshooting tips, and explains the underlying logic or reasoning behind the design. By doing so, it helps developers understand not just how to use our API or SDK, but also why it was designed the way it was.

Writing good documentation is an art in itself. It requires a deep understanding of the subject matter, the ability to explain complex ideas in simple terms, and a commitment to keeping the documentation up-to-date as the API or SDK evolves.

Design for Scalability and Flexibility

In his book, Ousterhout encourages us to be forward-thinking. Our APIs and SDKs should be designed with future scalability and adaptability in mind. This means that they should be capable of handling increased demand, and flexible enough to be adapted to new scenarios with minimal effort.

Designing for scalability and flexibility often involves making strategic decisions. We might have to choose a more complex design now, to ensure that our API or SDK can handle future growth or changes. However, these decisions should always be made with the user in mind. After all, an API or SDK that can scale and adapt to changing needs is ultimately more useful to the user.

Robust Error Handling

Ousterhout maintains that error cases are part of the normal flow of control and should not be treated as 'special' cases. This perspective encourages us to design robust error handling mechanisms in our APIs and SDKs.

Effective error handling requires clear, informative error messages and consistent procedures for handling different types of errors. This ensures that when things go wrong, developers can quickly identify and resolve the issue.

However, robust error handling is not just about reacting to errors; it's also about preventing them. By validating input data, checking for potential issues, and providing clear, helpful error messages, we can help developers avoid errors in the first place.

Feedback is Key

Lastly, Ousterhout's philosophy is about continuous learning and improvement. It's about inviting user feedback and using it to refine and improve the design. It's about seeing our work not as a static creation but as an evolving tool that grows and improves with user input.

Encouraging feedback requires open, clear communication channels. It requires a willingness to listen to criticism and learn from it. It also requires a commitment to iterative improvement, constantly refining and improving our design based on user feedback.

Ousterhout's philosophy, when applied to API and SDK design, promises a rewarding journey. It leads to the creation of powerful, intuitive tools that understand the user's needs and elevate the developer experience. So let's embrace this philosophy and commit to creating better software, one line at a time.