Functional Specification Document: What Is It and How To Create It?

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When approaching a software development company with a project in mind, it’s good to provide a document listing all the requirements. Development teams use it to prepare a rough estimation of the project and, once it’s launched, an in-depth needs analysis.

One of the documents you need to include is a functional specification.

Read this article to find out why you need a functional specification document, what it is, who is it for, and how to write one that guarantees the success of your project.

What is a functional specification?

A functional specification works like a blueprint that helps the development team to understand how an application will function. It describes the user experience step by step.

A functional specification basically tells developers what features they need to build and why. It also helps all the stakeholders involved in the process to work through their often diverging opinions by focusing on a set of goals.

Why write a functional specification?

It’s easier to design a product using words than code. It takes a few minutes to come up with some alternatives to revise and improve a design that is written down. The same may take weeks when it comes to coding an iterative design.

A functional specification ensures that developers are working on the right functionalities from day one and greatly reduces the risk of project failure.

Who is it for?

Functional specification documentation is intended for all project stakeholders. It tells developers what features they need to build and how, but it’s a good idea to share it with the entire team for better transparency and collaboration.

Writing a functional specification

Now that you know what a functional specification is and why it’s a good idea to write it, here are a few tips to help you get started.

A specification is a text document that identifies stakeholders, its own history and potential previous approvals. Apart from that, a functional specification needs to include:

  • Project scope – the goals, deliverables, features, tasks, costs, and deadlines of the project.
  • Risks and assumptions – all the considerations that may impact the functional design of the product.
    Product overview – that’s where you explain how your application will solve a specific problem of your target audience (displayed on, for example, sitemaps, screen flows, wireframes)
  • Use cases – that’s where you place functional requirements in the context of a user action. This point is essential because you’ll be showing what happens in the app from the user perspective.
  • Requirements – critical features of your product that answer the question: what does your product do?
  • Configuration – steps required to configure a product (for example, setting up a user account)
  • Non-functional requirements – your document can also list nice-to-have features that aren’t at the core of your product.
  • Error reporting – explain how your product will handle errors or exceptions. What kind of messages should be displayed and options presented to users on the UI?

Note that your specification doesn’t need to include each and every one of these points. Depending on your project and team, the functional specification document may take on different forms.

Write detailed use cases

Let’s examine this point in detail. In theory, we all know what use cases are. A use case describes the behavior of a system when the user performs an action. But what should a use case include?

Here are a few essential elements every use case should have to provide developers with maximum context for developing features:

  • Name – that’s right, you need to come up with a distinct name for every use case. That’s how you’ll be able to navigate use cases once you write up many of them.
  • Description – every use case needs a detailed description where you specify several things:
    • Preconditions – what is the state of your application at the onset of the use case?
    • Actors – who are the users involved in the use case and what problem they want to solve?
    • Basic flow – the step-by-step flow in your application.
    • Alternate flow – alternative flow provided the user chooses an option.
    • Exception flow – another type of flow that follows an exception to the basic flow described in your use case.
    • Post conditions – the state of your application after the user performs the action.

Engage the entire team

It’s smart to create a functional specification together with all critical members of the project. Their input will help you decide which features are core and need to be developed first, what the user experience will look like, and how the application will deal with errors. The more people review it, the better.

With that document in hand, you can be sure that developers do a great job when creating your product.

Are you looking for a team of skilled software developers? Get in touch with us; we have ample experience in delivering various IT projects.

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