Software Design Document: Templates & Examples

Instructor: David Gloag
The requirements have been gathered and the functional specifications have been created. In this lesson, we'll take a look at the next developmental step, the software design document.

The Details of Design

Software doesn't magically appear. There is no spell that can be cast to achieve a viable product. It takes hard work, dedication, and a unified vision. As a result, efforts are made to clearly document each step of the effort, in the hope that it will bring all interested parties to the same page. It starts with a document of requirements, a set of WHAT's for the project, moves on to a document of specifications or preliminary HOW's for the requirements, and then continues on to document that contains the details of the HOW's. This is where the software engineers get down to the nitty gritty. The process is called software design. And the place that contains this information is the software design document.

What is a Software Design Document?

A software design document is a detailed, multi-page description of how a software-based product will be provided. It is written by a software developer, or group of developers, and details how a product will be built, feature by feature. The purpose of the document is to provide the developers with additional details to those provided in the functional specification. If you think of a functional specification as a thousand-foot view, then a software design document is a hundred-foot view. As an example, if the functional specifications say that the MAC platform will be supported, the software design document will indicate which versions of the MAC operating system. If the functional specifications say that Visual Studio will be used as the development platform, then the software design document will indicate which version of the environment. And if the functional specifications say that sorting will be used, the software design document will indicate that a quicksort will be used rather than a heap sort, or bubble sort.

What Does a Software Design Document Look Like?

Like requirements and functional specification documents, software design documents can vary depending on the project. In fact, no two software design documents are alike. However, they usually take the same general form as their corresponding requirements and functional specification documents. This is done for tracking purposes, as it allows features to be traced back to requirements. Regardless of the specific form, software design documents typically have the following 3-level structure:

Software Design Document Layout

Please note that the section headings (those items of the form X and X.X), will vary somewhat depending on the project being undertaken. Also note that heading 3.5 would likely be a number of headings that are specific to the project. They have been condensed here for brevity. The actual Feature Design Descriptions (those items of the form X.X.X), will be discussed in the next section.

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