How can you ensure maintainable and extensible system decomposition?

2 Apply the principle of separation of concerns

One of the main principles of system decomposition is separation of concerns, which means dividing a system into distinct components that have a single responsibility and a well-defined interface. This way, you can isolate the different aspects of the system, such as data, logic, presentation, communication, etc., and reduce the dependencies and interactions between them. Separation of concerns also helps to improve the readability, testability, and maintainability of the system, as you can focus on one component at a time and change it without affecting the others.

3 Choose an appropriate decomposition strategy

When decomposing a system, you can apply various strategies based on the criteria and level of abstraction used. Functional decomposition breaks down a system into components based on the functions or features they provide, such as an online shopping system divided into product catalog, shopping cart, payment, and order processing. Data decomposition divides a system into components based on the data entities or structures they manipulate, while concurrency decomposition separates a system into components based on the parallel or concurrent execution of tasks. Layered decomposition breaks down a system into components based on the level of abstraction or hierarchy they belong to. You can choose one or more of these strategies to decompose your system, or even create a hybrid decomposition that meets your specific needs.

4 Design clear and consistent interfaces

The interface of a component is the way that it communicates and interacts with other components. It defines the inputs, outputs, parameters, methods, events, and protocols that the component expects and provides. A good interface should be clear, consistent, simple, and stable, so that it is easy to understand, use, and integrate. It should also hide the implementation details and internal state of the component, so that it is decoupled from the other components and can be changed without breaking the system. You can use various tools and standards to design and document your interfaces, such as UML diagrams, API specifications, contracts, etc.

5 Apply design patterns and best practices

Design patterns are reusable solutions to common problems in system design, providing a template or guideline that can be adapted and applied to a specific context. They capture the best practices and knowledge of experienced designers, helping you to avoid common mistakes. Examples of design patterns that can assist with system decomposition include Modular Design, Microservices, Facade, Adapter, and Composite. Modular Design involves designing the system as a collection of independent and interchangeable modules with high cohesion and low coupling. Microservices involves designing the system as a collection of small and autonomous services that communicate through lightweight and standard protocols. Facade involves designing a component that provides a simplified interface to a complex subsystem. Adapter involves designing a component that converts one interface to another. And Composite involves designing a component that represents a group of components as one. These are just some of the many design patterns you can explore and apply for system decomposition.

6 Refactor and evaluate your system decomposition

System decomposition is not a one-time activity, but an iterative and evolutionary process that should be continually evaluated to ensure it meets system goals and requirements, and does not introduce any issues or inefficiencies. To refactor and evaluate your system decomposition, you can use various techniques and metrics such as code reviews for examining code quality, testing for verifying functionality and performance, code analysis for measuring characteristics and properties, and architecture evaluation for assessing the quality of your system architecture. By applying these techniques and metrics, you can identify and resolve any problems or shortcomings in your system decomposition, thus improving its maintainability and extensibility.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?