Engineering
Software Design Docs
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A software design doc - also known as a technical spec, or an RFC (request for comment) - is a description of how you plan to solve a problem. It usually includes the goals of the project, a proposed overall architecture, and considerations including alternatives considered.
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What You'll Learn
What is a Software Design Document?
A Software Design Document (SDD) is a comprehensive guide that outlines the design of a software project. It serves as a blueprint for developers, stakeholders, and other team members to understand the project's architecture, functionality, and requirements.
Scaling Engineering Teams via Writing Things Down and Sharing - aka RFCsScaling engineering teams can be challenging. Gergely recommends a simple process for writing down plans before building anything new. Teams should capture their plans in short documents and have a few people approve the plans before starting work. Importantly, teams should send these planning documents to all engineers in the company to comment on. This process of writing things down creates Accountability and leads to more thorough decisions. Having others review the plans helps ensure a consistent engineering bar across the organization and allows knowledge to spread. The author notes that this RFC process has scaled well at Uber from tens of engineers to thousands.
Common Software Design Docs Challenges
These are common challenges people face when gaining expertise in software design docs. Tackling these challenges head-on can help you learn this skill quicker.
I'm a senior software engineer leading a team of developers. I often receive design documents from team members that lack clarity and coherence. The documents are either too high-level, missing important details, or too detailed, making them difficult to understand. This leads to misunderstandings and delays in the development process. How can I guide my team members in creating design documents that strike the right balance between high-level overview and implementation details?I'm a software engineer working on a distributed team. We rely heavily on software design documents to communicate and get alignment. However, due to different time zones and communication challenges, it's often difficult to get timely feedback and clarification on the design documents. What should I do to make sure that our design docs are serving us well in this distributed team setting?Add your own to track your progress and inspire othersHow to Write Software Design Docs
Writing a Software Design Document requires a structured approach that involves identifying the project's goals, defining the scope, creating a high-level design, and breaking it down into detailed requirements. Collaboration among team members, stakeholders, and subject matter experts is essential in creating an effective SDD.
How to write a good software design docAngela covers: • Why teams should write design documents • What to include in a design document • How to write one • The process before and after writing one.
Writing a High Level DesignWriting a high level design document should start with requirements and a domain model. The domain model, created with the product owner, defines the key concepts and how they relate. This model forms the foundation for the rest of the design. The document should also include a system diagram showing the system components and how they interact. Scenarios and use cases are used to exercise the domain model and refine the design. Failure scenarios should also be considered to identify potential flaws and improve resilience. The design is iterative, with feedback incorporated to refine the domain model, system diagram and other sections.
What to Do After a Software Design Doc is Written
After writing a Software Design Document, it's important to review and refine it continuously to ensure that it aligns with the project's objectives. The SDD should be shared with stakeholders and team members for feedback and revision. It should also be updated regularly to reflect any changes in the project's scope or requirements.
Learning to like design documentsDesign documents can help clarify your thinking before starting a project and catch potential issues early. However, getting useful feedback can be hard as few people read the whole thing. Julia found it helpful to talk through her design document to get feedback. Design documents also help track how requirements change over time. They are not meant to predict everything, but rather help adapt as issues arise.
Software Design Doc Case Studies
Tech Design at RiotRiot uses a Request For Comment (RFC) process to establish technical standards and best practices in an autonomous way. Engineers write up proposals and circulate them to get feedback from others. They are free to incorporate or ignore the feedback as they choose. Adopting an RFC means teams agree to follow its guidance where applicable. Over 425 RFCs have been created covering every aspect of Riot's technology stack. RFC 100 led to a standard service identification protocol used across the company to identify running services.
Design Docs at GoogleDesign docs are informal documents that software engineers at Google create before coding a project to document the high level design strategy and key decisions. They help achieve consensus around the design, ensure consideration of cross-cutting concerns, and scale knowledge of Senior Engineers. There is no strict format but a useful structure includes context and scope, goals and non-goals, the actual design, alternatives considered, and cross-cutting concerns. The ideal length is around 10-20 pages. Design docs are updated during implementation when the initial design changes, and they serve as a useful reference for maintaining and learning from the system over time.
Software Design Docs Cheat Sheet
Here is a quick reference for the top 5 things you need to know about Software Design Docs.
- Step 1: Define the Purpose and Scope
- Clearly articulate the goals and objectives of the software design document.
- Specify the intended audience and stakeholders.
- Define the scope of the document, including the features, modules, or components to be covered.
- Step 2: Document the Architecture and Design
- Describe the overall architecture of the software system.
- Document the key design decisions, patterns, and frameworks used.
- Specify the interfaces, data flows, and interactions between different components.
- Step 3: Provide Detailed Functional Specifications
- Define the functionality and behavior of the software system.
- Document the input and output requirements.
- Specify the user interface, user interactions, and system responses.
- Step 4: Document Non-Functional Requirements
- Capture the performance, scalability, security, and reliability requirements.
- Specify any constraints, dependencies, or external integrations.
- Address error handling, exception handling, and edge cases.
- Step 5: Include Supporting Documentation
- Provide diagrams, flowcharts, or wireframes to illustrate the design.
- Include API documentation, data models, or database schemas.
- Attach relevant reference materials, research findings, or technical specifications.
- Step 1: Define the Purpose and Scope
Frequently asked questions
How can I ensure that my software design document is easy to understand and maintain?
Focus on clarity, consistency, and organization. Use clear language, avoid jargon, and provide explanations for any technical terms or concepts. Organize the document into logical sections and use headings, subheadings, and diagrams to make it easy to navigate. Additionally, keep the document up-to-date by regularly reviewing and updating it as the software design evolves.
How do I involve stakeholders in the software design documentation process?
Start by identifying the key stakeholders, such as product managers, developers, testers, and end-users. Then, engage them in the design process through meetings, workshops, or interviews to gather their input and feedback. Make sure to communicate the design document's purpose and structure clearly and provide opportunities for stakeholders to review and comment on the document throughout its development.
How do I balance the level of detail in my software design document?
Balancing the level of detail in your software design document requires considering the needs of your audience and the complexity of the software. Provide enough detail to enable developers, testers, and other stakeholders to understand the design and make informed decisions, but avoid including unnecessary information that could make the document difficult to read and maintain. Focus on the most critical aspects of the design, and use diagrams, tables, and other visual aids to help convey complex information more clearly.
Software Design Document Templates
Software Design Document Templates provide a framework for creating an SDD that follows industry best practices. There are several templates available, each with its own structure and format. Choosing the right template depends on the project's complexity, size, and requirements. Templates can save time and effort in creating an SDD, but they should be customized to fit the project's unique needs.
On Writing Tech SpecsChuck covers: • The benefits of writing a tech spec • What happens in a scenario without a tech spec • An example tech spec • How to Write a Tech Spec, with 17 components to consider