Software design is the process of defining the architecture, components, interfaces, and other aspects of a software system. It involves making decisions that affect the quality, functionality, performance, and maintainability of the software. But how can you document and justify these decisions, and why is it important to do so?
Documenting design decisions is a way of communicating the rationale, assumptions, trade-offs, and alternatives behind your design choices. It helps you and your team to keep track of the design evolution, avoid duplication or inconsistency, and facilitate reviews and feedback. It also helps other stakeholders, such as clients, managers, testers, or users, to understand the design goals, constraints, and implications. Documenting design decisions can also serve as a reference for future maintenance, enhancement, or reuse of the software.
I was involved in documenting software design decisions for a long time and actually, there are several additional key points to highlight when discussing the importance of this essential step: 1- Facilitates team collaboration and knowledge sharing. 2- Mitigates risks and uncertainties early in the project. 3- Supports quality assurance and testing processes. 4- Ensures alignment with business goals and requirements. 5- Helps meet regulatory compliance when necessary. 6- Provides historical context for future reference. 7- Aids communication with clients and stakeholders. 8- Encourages innovation and creative thinking. 9- Maintains consistency in design and development. 10- Contributes to long-term software sustainability and success.
When determining what design decisions to document, it is essential to consider the context, scope, and complexity of the project. Generally speaking, some of the design decisions worth documenting include the high-level architecture and design patterns of the software system, key functional and non-functional requirements, design principles and guidelines, design trade-offs and alternatives that were considered and rejected, as well as design assumptions and dependencies. These elements provide insight into the use cases, scenarios, user stories, performance, security, reliability, scalability, coding standards, naming conventions, best practices, pros and cons of different approaches, risks associated with each option, costs and benefits of each decision, input and output data needed for the project, platform requirements for development or deployment, environment considerations such as tools or frameworks used in the project.
I would say, the level of detail and documentation format can vary based on project size and complexity. It's essential to strike a balance between providing sufficient information to guide the development process and avoiding excessive documentation that may become burdensome.
There are various formats and tools for documenting design decisions, from informal to formal, and from textual to graphical. Design decision records (DDRs) are short and structured documents that capture a single design decision and its context, rationale, alternatives, and consequences. They can be stored in a repository or a wiki and linked to other documents or code artifacts. Design diagrams are graphical representations of the design elements and their relationships, such as UML diagrams, ER diagrams, flowcharts, etc. Design documents are comprehensive and detailed documents that describe the overall design of the software system and its components. These documents are useful for documenting the design goals, requirements, principles, patterns, components, interfaces, etc. All of these formats are useful for capturing significant, controversial, or likely-to-change design decisions as well as documenting the structure, behavior, and interactions of the software system at different levels of abstraction.
Justifying design decisions is the process of providing evidence and arguments that support your design choices and convince others that they are valid, appropriate, and optimal. This involves analyzing the design problem and its context, such as the requirements, constraints, stakeholders, etc., evaluating the design options and their trade-offs, such as the advantages, disadvantages, risks, costs, benefits, etc., comparing the design options against the design criteria, such as the quality attributes, standards, best practices, etc., and selecting the best design option based on the analysis, evaluation, and comparison. To complete this process you must explain the reasons why you chose this option and document your justification and decision. Finally, you should present it to the relevant audience such as your team or a client or manager.
Improving design decisions is the process of refining, revising, and validating your design choices based on feedback, testing, and learning. This involves seeking feedback from different sources, such as peers, reviewers, clients, and users; testing and measuring the design outcomes; identifying and prioritizing design issues and gaps; applying design changes; and repeating the cycle until expectations and requirements are met. Documenting and justifying design decisions is crucial for software design as it helps communicate, clarify, validate choices, and improve them over time. It also allows others to understand, appreciate, and collaborate on your design. By following tips and techniques in this article, you can document and justify your design decisions with greater efficacy.