Functional Specification: Definition & Examples

Instructor: David Gloag
As businesses are looking to satisfy the requirements outlined for their customer projects, formalized methods have been adopted to ensure timely delivery. In this lesson, we'll take a look at an important development step, the functional specification.

The Next Step

Commerce drives everything! Customer requirements are satisfied by businesses each and every day. The formality of the relationship (read that as legality) means that structured documentation is created that clearly describes the interaction, particularly for complex undertakings. Do you think that companies like Amazon will spend millions of dollars for software and equipment from Dell without formal documentation? Not likely. The process starts with a requirements document or documents, which provides a detailed list of what must be done or provided. But where does it go from there? Surely, there is more to the process? In fact, there is. The next step is just as formal, and takes form as a functional specification.

What is a Functional Specification?

A functional specification is a multi-page document that describes how the product or service will be provided. It is written by the vendor, and matches up detail by detail with the items listed in the requirements document. The purpose of the document is to provide the developers with the specifics of the implementation. For example, it will describe the platforms the product/service will support, the development environment and tools to be used, and the technologies to be included during implementation. It is important to note that, while detailed, this document is nowhere near as formal as its requirements counterpart.

What Does a Functional Specification Look Like?

Like requirements documents, functional specifications can vary depending on the author and the audience. However, they usually match up in form with their corresponding requirements document. This is done for consistency and to ensure nothing is missed. Regardless, most functional specifications have the following 3-level structure:

Functional Specification Outline

Please note that the section headings (those items of the form X and X.X) will vary somewhat depending on the project being undertaken. The actual specifications (those item of the form X.X.X) will be discussed in the next section.

How Does Each Specification Relate to the Corresponding Requirement?

As mentioned, specifications correspond directly to a specific requirement. They are paired by number and provide a more detailed view of the requirement they are matched with. Think of it this way: a requirement is the tip of the iceberg and the specification is what's under the water. It is also important to note that one requirement may map to more than one specification. Let's look at an example. Say we have the following requirement:

  • 3.3.2 The application shall provide a main window that all user activity is launched from.

Then the corresponding specifications might be:

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