How To Create A Software Design Document

Most software developers prefer to rush through the process of documenting design requirements, or even avoid it altogether were it is possible. They would prefer to jump right into building the code and progressing towards rolling out the finished product. However, building a whole software product or a set of them, without a software design document can be disastrous. A software requirement document, or a software design document, is a solid record of specifications and various details that serve as a blueprint throughout the project.

A software design document clearly lays out what are the requirements, expected features, desired functionalities, etc. from the software and becomes a reference point that the entire software development team can follow. And when the software is being built for an external client, the software design document takes on even more important because it ensures that both the client and the software development company agree on the deliverables so that there’s no confusion during the project or at the time of the release/ handover. That’s why, even if writing a software design document may seem like a boring chore, documenting design requirements and creating software design documents is a must for every software developer.

Let’s take a quick look at what is a software design document and the essential elements that each such document must carry.

What is a Software Design Document?

A software design document is known by different names such as a software design specification or technical specification documents or a software requirement document. It is a highly detailed document that describes the overall architecture of a software product that needs to be created. According to the IEEE, a software design document is "a description of software created to facilitate analysis, planning, implementation, and decision-making." Think of it as a guide or a blueprint that serves the software architects (the coders and developers) and helps them understand how they need to build a software product based on a set of technical requirements.

And who creates this necessary document? It is typically the project managers and experienced software developers who create a software design document and ensure that all the stakeholders understand the specifications of the software.

Why do we need Software Design Documents?

Imagine what would happen if you embarked on a long road trip without any navigation or a map to guide you? Or an architect decided to construct a whole house without a blueprint to guide him and his team? Software design documents are an important way of looping everyone into the process who is involved in the product. It is for everyone to understand what is possible, what is not possible, and the system that will be designed by giving them a stable reference point that describes all parts of the software and how they will operate.

For the internal development team, it serves as a great way to plan out the entire system architecture clearly. Developers and project managers can go through every possible roadblock or possible gap that can hamper the project. It unifies project-related information and allows for discussing all significant questions arising between stakeholders and developers.

A software design document ensures that the product is built meeting the needs and is on par with what was agreed upon before the inception of the software. It also serves as a checkpoint for clients to confirm if the software development company has delivered as planned.

What Impacts the Type of Software Design Document?

The documentation type that a software development team will create will depend a lot on the chosen software development methodology. That’s right. We’re talking about the traditional Waterfall Methodology and the more recent Agile Methodology. Each is unique in terms of accompanying documentation.

The waterfall method is linear, with distinct goals for each development phase. When this approach is being used for software development, much time is spent on product planning in the early stages of the project, and detailed documentation is built before any of the subsequent development stages begin. Development teams create an extensive overview of the main objectives and can plan what will be the working process, ensuring precise budgeting and time estimates. Of course, as the past decade has shown us, the waterfall methodology is not effective for long-term development as it doesn’t account for possible changes and contingencies on the go.

The agile method for software development is based on close collaboration between developers and the client and provides both scalability and the flexibility to respond to changes faster. The agile method is highly iterative, and each iteration, i.e., a large change in the specifications or improvement/new requirements, involves planning, analysis, design, development, and testing. The agile method doesn’t require comprehensive documentation at the beginning because the project involves many changes as it evolves. The idea is to produce documentation with information that is essential to move forward when it makes the most sense.

Now let’s look at what an ideal software design document should hold.

What Goes in the Software Design Document?

Here are the details that a typical software design document contains:

Title:

Title of the document

Introduction:

Overview of the entire document and its purpose

Project Overview:

A general description and functionality of the software

Design Considerations:

List out the roadblocks that need to be addressed before creating the software. These would include details like:

• Any possible wrong assumptions or any dependencies
• General constraints that could impact the design of the software
• Goals and guidelines for the design of the software
• Development methodology that will be used

Architectural Strategies:

Strategies that will be used will affect the system.

System Architecture:

A high-level overview of how the functionality and responsibilities of the system have been partitioned and assigned to subsystems or components.

Policies and Tactics:

Design policies and tactics that do not have wide architectural implications, i.e., they would not significantly affect the overall organization of the system and its high-level structures.

Detailed System Design:

Most components described in the System Architecture section will require a more detailed discussion. Other lower-level components and subcomponents may also have to be described.

Roles and responsibilities:

Information about participants, including a product owner, team members, and stakeholders, with clearly defined responsibilities and the planned release goals for each of the team members.

Assumptions:

List of technical or business assumptions that the team might have.

Architecture and Design Principles:

Describes the guiding architecture and design principles with which you will engineer the product.

Diagrammatic representation of the software/ product:

Diagrams that will help understand and communicate the structure and design principles.

Source code document (optional):

A source code document is a technical section that explains how the code works.

Source code documents could include details like:

• HTML generation framework and other frameworks applied
• Type of data binding
• Design pattern with examples
• Security measures
• Other patterns and principles

Quality assurance:

The most common ones are:

• Test strategy
• Test plan
• Test case specifications
• Test checklists

Glossary:

A comprehensive list of defined terms and concepts used throughout the document.

Types of Software Design Documentation

The key objective of such documentation is to ensure that all the stakeholders involved have a common objective and are aligned to a defined path. There are various types of software design documentation that serve this purpose.

Product documentation – Describes the product that is being developed and provides instructions on how to perform various tasks with it. There are two types of product documentation:

• System documentation – Refers to documents that describe the system and its parts. It includes requirements documents, design decisions, architecture descriptions, program source code, and help guides.
• User documentation – Refers to manuals that are mainly prepared for end-users of the product and system administrators. User documentation includes tutorials, user guides, troubleshooting manuals, installation, and reference manuals.

Process documentation – Includes all process-related documents created during software development and maintenance. For example, project plans, test schedules, reports, standards, meeting notes, emails exchanged, etc. While product documentation describes the product being developed, process documentation records the development process.

System documentation – Gives all stakeholders an overview of the system and the underlying technology. A system document will typically contain development requirements, architecture design, source code, validation docs, verification and testing, and a help guide for users. Sometimes it will also contain details about what a system should do, use cases, etc.

It Always Helps to Document

Any software development team must focus on delivering value to its customers, and high-quality documentation is as necessary as the software product being created. Good software documentation should be followed as hygiene and must be provided, whether it is a specifications document for developers and testers or software manuals for end-users. Comprehensive software documentation is specific, concise, and relevant, and should be restricted to what directly help achieve project objectives.

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