Functional Specification

In Software Development Life Cycle (SDLC), every stage and step carries, whether minor or major, great deal of importance and significance. From coding to user end testing, every stage is as momentous as the one before it. Likewise, the stage of documentation in Software Development Life Cycle (SDLC) is also as crucial as testing and programming. Though, mostly considered irrelevant and insignificant, documentation not only simplifies the development process, but also helps all the stakeholders in getting a clear understanding of the whole project. During the process of software development there are various kinds of documentations required such as Product Requirements Documentation, Architecture Design Documentation, Technical Documentation, Functional Specification Documentation, End User Documentation, and more. All these documents are needed by software developers and testers to collect and document different features and elements of the software, which are a vital part of software engineering. Therefore, to elaborate on the importance of documentation, here is a detailed description of one such type of documentation –Functional Specification.

What is Functional Specification?

Similar to the various types of documentation prepared during the process of software development, Functional Specification is prepared and completed to define the objectives of the project and the finished product. Also known as Functional Specs, Functional Specifications Document (FSD), Functional Requirements Specification, among other things, Functional Specification’s main purpose is to define the requirements to be implemented by the software solution. In short, in system engineering and software development, functional specification is a document that specifies the function that a system or component must perform. This document typically describes what is needed by the system user as well as requested properties of inputs and outputs. A functional specification is the more technical response to a matching requirements documents, such as, the product requirement document. Moreover, if the product requirement document is the heart of the product, then the functional specification makes up as products brain, that is, it explains how everything works together in greater detail. Additionally, unlike the Product Requirement Document (PRD), the functional specification document can also be prepared or completed by the business analyst and technical leads. Moreover, these documents can vary in length and information as per the requirement of the project.

Categories of Requirements in Functional Specifications:

Written and prepared by business analyst or the technical leads, Functional Specification document provides a vast array of details about the software, its operations, functionality and deliverables. Moreover, this document includes information that the product must supply and defines its purposes. Functional Specification or functional spec also elaborates ways of judging the effectiveness of the product and makes sure that the criteria of software security and safety is met perfectly. Additionally, there are few necessary requirements that obligatory for functional specification as they are essential to it and can be considered the basic backbone of the whole document. These requirements define the way the information will be recorded and included in the document, that is, it categorizes the whole document under various requirements. Hence, these requirements are:

  1. Business Requirements – Contrary to its name, this is not only includes a brief detail about the business process and the need of the customized program report, but also provides functional and software requirements.
  2. Security Considerations – Here, the information provided is mainly regarding who all will have access to the program and the project. The basic focus here is to define the level of security, whether it is at the code level or country level.
  3. Data Requirement – This specifies the content or the structure that requires and constitutes high quality data.
  4. User Requirements -The information that defines the requirements of the users and the clients of the product. These are mainly written in a natural language and do not require any technical details.
  5. Operational Requirements-Provides information on technical environment, system integration, portability and maintainability.
  6. System Requirements – Written for developers and consist of detailed functional and non-functional requirements. Moreover, these are more clearly and rigorously specified.

Contents of Functional Specification:

After understanding the purpose of functional specifications and its requirements, it is of utmost importance for us to know the contents of this document. By gaining this information, one can create the functional specification document easily and include all the necessary information. Moreover, it will also allow developers and testers to collect all the required details of the project before it is started. This document records and provides information about the operations and activities that a system must perform and acts as the brain of documents that defines how everything works together in the software. Other details that are included in the functional specifications are:

  • Description of the data to be entered into the system.
  • It provides the descriptions of operations performed by each screen.
  • Work flow performed by the system are defined.
  • The system reports and other output are also included in the document with great details.
  • Information is provided on who can enter data into the system.
  • There is details about how the system meets the applicable regularity requirements.

Things to Avoid While Preparing Functional Specifications:

From providing details and information on various elements and features related to the software product, to helping developers, testers and other members of the project in understanding the development process, there are several roles of functional specification document during the Software Development Life Cycle (SDLC). Frequently, this document does not get the attention it deserves and is considered insignificant by the developers. Yet, it is a document that helps software engineers in saving development time and money as well as provides them an accurate time frame of the complete development process. Therefore, it is extremely necessary to prepare a functional specification document, while software engineers are building a new software or application. However, while preparing this document, the developers should be aware of all the aspects that should not be included in it. Furthermore, it should be clear that this document cannot replace or fulfil the need of other documents like, Product Requirements, Architecture Design Documentation, Technical Documentation, and more, as each document plays a crucial role and provide different information. Hence, here are some of the points that are not included in functional specifications:

  • It does not duplicate the information or detail that is already provided or mentioned in other documents.
  • It should not describe any design or implementation details that are not apparent to the user of the software. Only the internal design or implementation details should be described in the design stage of the project.

Benefits of Functional Specification:

As mentioned before, the advantages of creating a functional specification document are immense and innumerable. From describing the process and function to providing information about the various requirements, it helps a developer, tester and other people related to the project on various ways. Therefore, here is a list of some of the benefits and advantages of preparing a functional specification:

  • It assists software engineers in saving time and money.
  • Provides them an accurate timeframe of the whole process.
  • It will facilitate more accurate quoting.
  • Will allow transparency among all the stakeholders and members of the project.
  • Help non-technical members of the project in understanding various testing and development processes.
  • As functional specification is designed to be read by general audience, its biggest advantage is that it can be read and understood by individual with no particular technical knowledge.


As stated a before, the process of software development is an amalgamation of several activities, which are time and cost consuming as well as require great deal of efforts. It also include huge amount of documentation, which plays a very significant role in defining the whole process and its basic requirements. Functional Specification/ Functional Spec/ Functional Specification Document is one such document prepared during the process of software development by technical lead or a business analyst. Furthermore, the functional specification document is typically needed to evolve with the development of the software product, as it is impossible to specify some details at the time the project is initiated. The information that a functional specification contains are the document segment, which contains the company code, posting keys, vendors, etc., as well as the line items, which consists of document type and other similar information. In short, Functional Specification document describes properties of inputs and outputs, the blueprint for how one wants a particular application to look and work. Also, it details what the finished product will do and whom the user will interact with and what the product will look like. Hence, to create transparency among all the stakeholders of the project and to get a clear idea of the complete software development process, creating and preparing Functional Specification document is tremendously momentous.