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Functional Specification Document | The Complete Guide

Navdeep Singh Gill | 12 October 2024

Functional Specification Document | The Complete Guide
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functional specification document

Overview of Functional Specs

It's no secret that you must have clearly defined processes with frequent checkpoints and checklists for a project to succeed. But what does this process look like in practice? What work needs to be done, and how can we effectively measure our success? The answer is with a functional specification document. This document is one of the most important documents in any project or software development process (agile or waterfall). It's a document describing what the end-users want the system to do and not how it works. It includes input, output, control logic, storage, data handling, and security requirements.

 

user

Who is it for

This document primarily targets developers responsible for implementing the outlined specifications and requirements

clarity

Seek Clarity

It should be clear and comprehensible for all team members, including clients and stakeholders

responsibility

The benefits

Reduces the likelihood of miscommunication and coding errors during advanced phases of the project

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What is a Functional Specification Document?

It is a document that describes what the end-users want the system to do and not how the system works. It includes project scope, risk and assumptions, product overview, use cases, requirements, system configuration, non-functional requirements, and error reporting.  It is a document that specifies the functionality of a software system. It typically includes the specifications for all or most of the following:

  • User interface design and navigation

  • Data input and output formats

  • File formats, data types, and constraints

  • Database design, data access methods, and constraints

  • Programmatic interfaces for accessing external systems

  • Error handling procedures - Communication protocols for interfacing with external systems

  • Security requirements

Functional specifications can be created using a variety of techniques. These techniques can include:

  • Specifying how data is stored and processed by the computer system
  • Using a data model
  • Providing data representation
  • Designing the logical data structure that represents the data
  • Implementing an error recovery procedure
  • Working with XML
  • Adding business logic to a functional specifications document
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Purpose and Importance of the Document

It is the best way for stakeholders to understand the end product without knowing how it will work. A system's instructions explain how it should be used and what it should do. They are usually written by the person who designs the system.

 

The functional specification document is essential because it helps ensure that a system can be used in the way initially intended and that it will work with other programs and systems that may not have been considered during design.

 

Functional specifications are typically authored by a user, often the system designer. They outline the system's goals and objectives, expected use cases, requirements for data input and output files, any external devices that must be connected to the computer(s), and the necessary computing power for calculations.

 

Authors and Contributors

The person who creates the varies depending on the company's needs. The technical writer or product manager might work with developers to create a specification for a new program or features for an existing one.

 

In some cases, there are two people involved in creating this document: the product owner and the developer. The product owner is responsible for ensuring that the functional specifications make sense and that they meet user needs. The developer is responsible for defining a detailed description of how the system will be built with a complete analysis of all requirements.

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Key Components and Sections

It is a technical document that describes what the end-users want the system to do and not how the system works. It's a document that includes information about the project's scope, risk and assumptions, product overview, use cases, requirements, system configuration, non-functional requirements, and error reporting. It should contain:

  • Project Scope: The goals, deliverables, functions, tasks, costs, and schedules associated with the project. It includes a detailed description of what is expected to be done, delivered, and completed within the specified project schedule and budget. 

  • Risks and Assumptions: Risks and assumptions are potential variables and factors that can significantly affect a product's functional design. A detailed analysis of risks and assumptions is necessary to avoid potential roadblocks and ensure smooth project execution.

  • Product Overview: This is where you describe how your product solves a specific problem for your target audience. The product overview is typically depicted through various visual tools such as sitemaps, screen flows, and wireframes, which help to illustrate the user experience and provide a better understanding of the application’s key features and functionalities. 

  • Use Cases: To provide a comprehensive context for functional requirements, place them in the context of a user action. This approach is critical in effectively demonstrating the application’s functionality from the user’s perspective, providing a clear understanding of how the user interacts with the application and the outcomes of their actions.  

  • Requirements: Critical product features that answer the question: what does your product do? They are an integral part of the product development process and must be carefully considered in order to ensure that the final product meets the needs of its end users. 

  • System Configuration - These are the steps required to configure the product. For example, when setting up user accounts, system configuration includes defining login information, selecting appropriate security options, and setting user interface and preferences.

  • Non-functional Requirements - Documentation may list useful product features that are not considered part of the core functionality. These features are not essential for a product to work, but they play an important role in determining its overall quality and usability.  

  • Error Reporting - Describes how the product handles errors or exceptions. What messages and options should the user interface (UI) display to end users? These messages should be clear and concise and contain enough information to help users understand what is happening and what actions they can take to resolve the issue. 

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How to Write a Functional Document

A functional specification document describes what the end-users want the system to do and not how the system works. For example, you might create a specification for an app that helps people find public toilets in a city. It would include information about the input (such as GPS location) and output (public toilet location). Functional specs are often used in agile or waterfall development processes. To create a functional specification document, there are a few steps you need to take:

  1. Define your requirements for the project

  2. Identify functionality required by the project

  3. Design how this functionality will work

  4. Describe your requirements and design in an understandable format

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Summary

A functional specification document is a document that describes what the end-users want the system to do and not how the system works. It includes input, output, control logic, storage, data handling, and security requirements. It typically includes the specifications for all or most of the following. It is a technical document that describes what the end-users want the system to do. It's a document that includes information about the project's scope, risk and assumptions, product overview, use cases, requirements, system configuration, non-functional requirements, and error reporting. The developer is responsible for defining a detailed description of how the system will be built.

 

A functional specification document describes what the end-users want the system to do, not how it works. It would include information about the input (such as GPS location) and output (public toilet location). Functional specs are often used in agile or waterfall development processes.