How to Write a Software Design Document (SDD)?

A Software Design Document (SDD) is known by different names; it is often called a software design specification, a software requirement document, or technical specs. This is a detailed description of the overall architecture of a piece of software.

Why create one? Imagine this: your team spends several months building a software product, only to find out that it fails to solve the specified problems and looks nothing like what was originally envisioned. An frustrating scenario, isn’t it? Fixing such issues often feels like creating a new product from scratch—it demands significant time, effort, and resources. However, this situation could have been avoided with a well-prepared SDD.

In this post, explore the key components of an effective SDD and highlight how it serves as a foundational tool for successful software development. By clearly defining requirements, design choices, and architectural frameworks, an SDD not only fosters better communication among team members but also helps manage stakeholder expectations throughout the project lifecycle.

What Is an SDD?

An SDD is a document that should be created before any coding begins, and it answers the following questions:

• What problems is the software supposed to solve?
• What will it look like?
• What features will it include?

Essentially, it serves as a blueprint for the software, ensuring that the entire team is aligned and working towards the same goals. An SDD is the best way to ensure that all team members contribute to the right tasks and maintain focus throughout the development process.

An SDD becomes even more crucial when a software product is being developed for external customers. It provides a means for the customer and the development team to reach a mutual understanding of all major aspects of the project. Customers gain a clear view of how their requirements will be met, while the development team can accurately estimate the effort required for software development.

For example, consider a software development company tasked with creating a project management tool for a client in the construction industry. Before diving into the actual coding, the team prepares an SDD that outlines the project in detail.

In the document, they define the core problem: construction teams struggle to manage project timelines and allocate resources effectively. The SDD specifies that the software will include an intuitive dashboard, Gantt charts for tracking project timelines, and a feature for assigning tasks to team members. It also includes wireframes illustrating the user interface and a detailed list of functionalities, such as real-time collaboration and mobile access.

This SDD ensures that both the development team and the client have thoroughly reviewed and agreed upon the project’s scope and expectations. The client can confirm that their requirements are addressed, while the development team gains clarity on the time and resources needed to deliver the project. By keeping everyone aligned and on the same page, the SDD minimizes misunderstandings and helps ensure the delivery of a successful software product that meets the client’s needs.

Who Needs an SDD?

Writing an SDD is often one of the most challenging aspects of working on a project. Let’s be honest—hardly anyone enjoys doing it. For instance, software developers often prefer to dive straight into coding rather than taking the time to map out a strategy that will guide the team for the next several months. However, the benefits of having an SDD far outweigh the reluctance to create one.

Every role on a team relies on this document to prepare their work plans. For example:

• Project managers use the SDD to secure agreements from all project participants, from sponsors to the development team.
• QA testers rely on it to ensure the product functions as intended.
• Technical writers reference it to produce accurate user documentation.
• Developers use it to implement the specified features efficiently.

In short, the SDD serves as a cornerstone that ensures everyone is aligned and working towards the same objectives.

A detailed SDD is especially crucial in the following scenarios:

• Your product is highly complex (e.g., it includes numerous features or has different user interfaces for various user types).
• Your project involves multiple teams, requiring tight coordination.
• Your software is critical to your business, serving as a key source of leads or sales.

Benefits of SDDs

Creating a Software Design Document offers several key advantages that significantly enhance the development process:

• Clarity and Direction. SDDs provide a clear roadmap by outlining objectives and features. For example, a team working on an e-commerce platform can use an SDD to define user roles, payment processing systems, and inventory management. This ensures that all developers clearly understand what is expected of them.
• Improved Communication. SDDs serve as a communication bridge between developers, stakeholders, and clients. For instance, a mobile app development company can use an SDD to align the technical team with marketing and sales on the app’s features and its launch timeline.
• Risk Mitigation. SDDs help identify potential risks early in the process. Financial software companies, for example, often use SDDs to highlight regulatory compliance risks. This allows them to proactively implement necessary features and avoid costly changes later in development.
• Stakeholder Engagement. Clients can review the SDD to ensure their requirements are adequately addressed. For instance, in a government project, stakeholders can review the SDD to confirm that data security measures meet the required standards, leading to a smoother approval process.
• Resource planning and management. An SDD enables effective resource planning by providing accurate projections of costs and timelines. For example, an SDD for a project management tool under development can help companies secure funding from investors by showcasing a well-defined scope and timeline.
• Consistency and Standardization. The use of SDDs promotes consistency in design practices. Large software development companies often use standardized SDD templates to enforce consistent coding practices, facilitating seamless collaboration during software releases.

As demonstrated, SDDs significantly improve communication, mitigate risks, and streamline resource distribution, ultimately leading to more successful project outcomes.

What Should an SDD Include?

Here is what a software design document usually contains:

• Title. Title of the project.
• Authors and reviewers. This section lists the authors of the document. Reviewers may include stakeholders or other key participants.
• Introduction. General information about the project and its purpose.
• Roles and responsibilities. Information about all parties involved and their respective responsibilities.
• Overview. This section outlines the objectives of the software, how it will support business needs, and how it interrelates with other systems used in the company. It should also describe how the software fits into business processes and identify who will benefit from its creation.
• User interface. This section includes descriptions of the user interface and, if applicable, mockups or prototypes.
• Functions. A detailed description of the features and functions to be included, as well as those that are excluded. Precision is critical here to avoid overpromising or committing to unrealistic expectations.
• Scope. A description of the development process, often broken down into phases or iterations.
• Milestones. Key dates when the team will evaluate progress and review results.
• Glossary. A list of terms and concepts used in the document, ensuring clarity and understanding among all readers.
• References. Supporting or background information relevant to the project.

Here’s an example of a Software Design Document for reference: SDD Example.

How to Write an SDD: Language and Style

Writing a Software Design Document (SDD) requires choosing a language and style that ensure clarity, precision, and effective communication for all stakeholders. Below are key considerations to keep in mind:

Clear and Concise Language

• Use straightforward and uncomplicated words to express your ideas. Avoid technical jargon unless you are certain that all stakeholders understand the terms. For example, instead of saying “utilize,” simply say “use.”
• Keep sentences short and to the point to maintain the reader’s attention and make the document easier to read.

Consistent Terminology

• Define key terms and acronyms at the beginning of the document, and use them consistently throughout. This prevents confusion and ensures a shared understanding among all readers.
• For example, if you define “API” as “Application Programming Interface,” continue using “API” without reverting to the full term unnecessarily.

Formal Tone

• Maintain a professional and formal tone throughout the document to reflect the seriousness and credibility of the project.
• Avoid colloquial language or overly casual expressions. For instance, instead of saying, “We need to fix this,” say, “This is an issue that needs to be resolved.”

Active Voice

• Use active voice to make sentences direct and dynamic. For example, replace “The system will be updated by the developers” with “The developers will update the system.”
• Active voice clearly identifies who performs the action, reducing ambiguity and confusion.

Structured Format

• Organize the document into clearly defined sections and subsections with headings and subheadings. This improves navigation and readability.
• Use bullet points or numbered lists to present features, requirements, or steps, making the content easier to follow.

Visual Aids

• Incorporate visuals such as diagrams, charts, and tables to explain complex ideas or workflows. Visual aids enhance understanding and improve information retention.
• Ensure all visuals are clearly labeled, and reference them in the accompanying text to provide context.

Review and Revise

• After drafting the SDD, review it for clarity, coherence, and consistency. Seek feedback from team members and stakeholders to identify areas of confusion or misunderstanding.
• Revise the document based on feedback to ensure it meets the needs of all users.

Version Control

• Implement version control to track changes and updates to the SDD. Clearly label each version with dates and revision notes, allowing stakeholders to understand how the document has evolved over time.

By following these guidelines, the language and style of your SDD will ensure that the document is informative, accessible, and useful for all members of the development team and stakeholders involved.

A well-written SDD not only improves collaboration and minimizes misunderstandings but also contributes significantly to the success of the software development process.

Tools to Help You Write an SDD

An SDD should be a collaborative document as software development is a collaborative process as well. First of all, you should choose a documentation tool that will facilitate your writing workflow. Modern cloud tools, like ClickHelp, offer diverse and powerful functionality: it is not a problem if authors write different parts of a document simultaneously, if several reviewers leave comments, or if all team members work from different locations. I would say your SDD will become some kind of a transparent, centralized knowledge base for all team members if you use a suitable writing tool.

When working on a description of a user interface, don’t forget about wireframe tools. They are used to design apps, websites, software, etc. It is essential first to make a mockup of the interface and then to apply it to your product to create a better user experience. Here is the list of the most popular online wireframing tools:

• Canva. An online graphic design tool that allows you to create UX/UI wireframing. Its biggest advantage is its simplicity and intuitiveness, making it accessible even for non-designers.

• Miro. Is a visual online whiteboarding tool. This tool is great for the collaboration of remote team members.

• Sketch. Is a vector design program for designers to create prototypes, mockups, wireframes, etc.

• Lucidchart. Is one of the most popular cloud platforms for UX/UI design with a large variety of integrations with other software.

• Marvel. Is an all-in-one tool for professional UX/UI design.

• Cacoo. Is a diagramming tool that enables users to create wireframes, flowcharts, etc.

When choosing a wireframe tool, you are to pay attention to your specific use case and needs. There is no ideal tool for everything. Each tool works best for particular purposes.

Conclusion

Creating an informative SDD is halfway to creating a high-quality and helpful piece of software. It is a good opportunity to quickly figure out your team’s way without losing months wandering in darkness. I hope this post will give you new ideas and thoughts on how to write an SDD and customize this process to your product’s special features.

Good luck with your technical writing!
ClickHelp Team
Author, host and deliver documentation across platforms and devices

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