Andrew
Burak
CEO at Relevant

Your Guide to Writing a Software Requirements Specification (SRS) Document

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A software requirements specification (SRS document) describes how a software system should be developed. Simply put, an SRS provides everyone involved with a roadmap for that project.

It offers high-grade definitions for the functional and non-functional specifications of the software, and can also include use cases that illustrate how a user would interact with the system upon completion.

Note: Hire an expert business analyst to write a detailed SRS for your product. Request such a specialist by filling this form.

Why is an SRS Document Important?

Suppose you want to create a chat app with a specific appearance and functionality and would like it to be geared specifically to enterprises. You feel that you can cut out the extra features that commercial chat apps use to appeal to the public and focus on features that enterprises need. But you aren’t a developer.

So you need to outsource the development of the app. But you also need to make sure that whoever you hire to turn your idea into reality knows exactly what you’re trying to accomplish. Without all the details to finish the app, time and cost can quickly get out of hand. Developers can take a wrong turn and have to refactor the code if the finished product doesn’t match the picture you had in your head.

An SRS document forces you to put the idea down on paper to cover all these details. You must translate this idea into a language that developers understand. An SRS document describes what a client wants and what developers will provide. It is the written agreement on every detail of the app.

Having a clear set of requirements ensures that a development team creates software that meets the clients’ needs. An SRS will help with estimating the cost of work and covering the project scope. It also gives coders an idea of the tech stack they’ll need and helps them plan their work, but that’s not all:

  • Designers get project insights through SRS documents so they can match the design to the use case.
  • Testers get the guidelines for creating test cases that match the business’s needs.
  • End-users use the SRS to understand the software.
  • It provides investors with an overview of the system’s features so they can make investment decisions.

An SRS is important because it is a single source of information and expectations, which prevents misunderstandings between project managers, developers, designers, and testers.

What Does an SRS Include?

An SRS should have enough information for developers to complete the software described. It not only lays out the description of the software under development but also the purpose it will serve: what the software is supposed to do and how it should perform.

An SRS document typically includes these elements:

  • The purpose of the software being developed
  • An overall description of the software
  • The functionality of the software or what it is supposed to do
  • Performance of the software in a production situation
  • Non-functional requirements
  • External interfaces or how the software will interact with hardware or other software it must connect to
  • Design constraints or the limitations of the environment that the software will run in
software requirements specification SRS document components

The Difference Between Functional and Non-functional Requirements

Functional requirements are the goals of the new system you are designing. They describe the system and how it will function to help with a user’s tasks. They define how the system will respond to user input and have details on calculations, data input, and business processes. You can consider functional requirements a detailed description of the application’s features and the user’s needs. Without meeting the functional requirements, the system will not work.

While functional requirements specify what a system does, non-functional requirements describe how the system will do it. Non-functional requirements do not affect the application’s functionality. Even without meeting non-functional requirements, the system will perform the desired tasks.

Non-functional requirements are also important because they define the general characteristics that affect user experience. Instead of focusing on user requirements, they focus on user expectations and cover such topics as performance, security, reliability, availability, and usability.

How to Write a Software Requirement Specification Document

It is best to organize the process you use to write an SRS document by starting with a skeleton and general information on the software you’re developing, and finishing by adding details to flesh out your draft. Here are six steps involved in creating an SRS document:

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Create an Outline

The first step in the process is to create an outline for your SRS. You can create this yourself or use an existing SRS template as a starting point. Here is a basic example of an SRS outline:

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  1. Introduction
  2. Purpose
  3. Intended Audience
  4. Intended Use
  5. Scope
  6. Definitions
  7. Overall Description
  8. User Needs
  9. Assumptions and Dependencies
  10. System Features and Requirements
    1. Functional Requirements
    2. External Interface Requirements
    3. System Features
    4. Non-functional Requirements

Define the Purpose

Once you have an outline, you must flesh it out. Start with defining the purpose of the product in the introduction of your SRS. Here you will describe the intended audience and how they will use the product. Here’s how you should structure the purpose:

  • Define the product’s scope
  • Describe the value it will deliver
  • Show who will use the software
  • Detail how it will help with the intended users’ job

Give an Overview

After defining the product’s purpose, summarize how it will work. Here you will give a general description of the software’s features and how they fit the user’s needs.

You will also describe the assumptions you are making about the product’s functionality and anything it depends on in the current tech ecosystem.

Describe Functional and Non-functional Requirements

Now that you have written the general information, it is time to get more specific. Completing your overview before you work on functional and non-functional requirements gives you a reference to make sure you meet the user’s basic needs while you fill in the details.

This detailed description of the system’s requirements is the most essential component of an SRS document. Describe the functional requirements in enough detail so developers can get to work and the non-functional requirements like security specifications and performance.

Here is where you add use cases to vividly describe how a user will interact with your system. It is where your project’s objectives are detailed and will measure how the project is progressing during development.

Add Supplemental Details

The last step in creating the draft of your SRS document is adding any details that could help developers finish the job in the form of appendixes, glossaries of terms, and references.

Get Approval

Once you have added enough details to the SRS to describe what the system is supposed to do, it is time to have the stakeholders approve the document.

You will most likely have to make a presentation to the people involved in the development process. They may ask for changes, and you will have to update the SRS document based on stakeholder feedback before final approval.

This is a good sign. It means both developers and stakeholders are making the document more precise, so the project is less like to go off track.

How to Write Software Use Cases in an SRS

A use case describes how a user will interact with the system. It will describe the product from the end user’s point of view in a simple story format. Writing out use cases forces you to think through what users will do with the software and how it will respond. It is the real-life visualization of the functional requirements.

Here are steps you can follow to write a use case:

  1. Describe your product’s end users.
  2. Focus on one of these users.
  3. Break this user’s interactions down into use cases. Each interaction is a use case.
  4. Describe the sequence of events for each use case.
  5. Write a detailed description of the user’s actions and how the system should respond.
  6. Expand each use case with alternate user actions and system responses.
  7. Repeat 1-6 for each type of end-user.
How to Write Software Use Cases in an SRS

What are the characteristics of a great SRS?

There are specific characteristics that every SRS should have. By reviewing this list and comparing it to your SRS, you can ensure that it will be a useful document for all stakeholders.

Explicit

An SRS document should be easy to understand. Nothing should be vague, so there are no misunderstandings between stakeholders.

Measurable

The requirements in your SRS document need to be measurable, so the finished product can be validated and verified against the specifications.

Complete

An SRS document should have enough information for your development team to finish the product and for testers to validate that the product meets the user’s need without bugs.

Viable

The requirements should fit the reality of the current environment, including the budget, timeline, and technology. They shouldn’t depend on upcoming technological breakthroughs.

Flexible

Because things could change in the working environment, your SRS document should be flexible enough to allow for updates. Don’t add redundant information to multiple sections that have to be updated with each change.

Verifiable

Everyone on the development team should have access to the document so they can reference it as frequently as necessary. Requirements need to be precise so that team members do not have to ask for more details. They should all be available in the SRS document.

Consistent

The requirements should fit each other. One section of your requirements document should not conflict with another. The document should be formatted consistently and used the same terminology throughout.

No Implementation Constraints

An SRS document should be detailed enough to finish the job, but should not be overly specific, because that might restrict development. A lot of development depends on third-party services that developers have no control over.

Accurate

Goals in a requirements document should be precise to avoid confusion. Avoid the following:

  • Loopholes: “The application should load in 3 seconds if it can be done.”
  • Ambiguity: “The MVP product should be released as quickly as possible.”
  • Subjectivity: “The UI should be user friendly.”
  • Superlatives: “This should be the best application in its class.”
  • Comparative: “This application should be better than Slack.”

A Software Requirement Specification (SRS) Example

Here is a trimmed down example of an SRS document for an enterprise chat app called eChat:

Introduction

This document details the project plan for the development of “eChat.”

It is intended for developers, designers, and testers working on “eChat” as well as project investors. This plan will include a summary of:

  • how the system will function
  • the scope of the project from the development viewpoint
  • the technology used to develop the project, and
  • the metrics used to determine the project’s progress
  • Overall Description

Companies need remote communication tools, especially now that more people are working from home. The problem is that most companies end up using multiple applications to accomplish this: one for text chat, one for video chat, and one for conferences and meetings. “eChat” will solve this problem by combining these features in one application.

Customers

The customers will be enterprise companies. It will not target the general public.

Functionality

  • Users should be able to sign up with enterprise LDAP accounts.
  • Users should be able to create ad hoc chat groups comprising sets of users and send private messages to individual users.
  • Users should be able to have text chats that they can break into threads.
  • The application should be able to handle group video chat of up to 100 users at a time.

Platform

The application will be developed in React Native to enable the creation of a web-based application, an iOS mobile app, and an Android mobile app.

These applications will connect to a REST API built with .NET Core to store and retrieve data from a MySQL database.

Authentication will be through existing LDAP installations.

Development Responsibilities

The developers on the “eChat” team will be responsible for writing all the code for the application, developing the database, and managing releases.

User Class and Characteristics

There will be a class of users called admin that will have permissions to access all functionality of the app, including:

  • Creating channels where multiple users can interact
  • Making these channels public to the entire company or private for a group of people
  • Deleting these channels
  • Archiving these channels

Standard users will have access to all functionality of the app except those listed above.

System Features

Functional Requirements

  • Users should be able to create ad hoc chat groups comprising sets of users and send private messages to other users.
  • Users should be able to have text chats that they can break into threads.
  • Chats should be able to be archived indefinitely so users can reference past chats.
  • Users should be able to upload files to chats for reference.
  • External Interface Requirements

User Interfaces

  • Front-end software: React Native
  • Back-end software: .NET Core
  • Database software: MySQL
  • LDAP connection: Authentication in an enterprise environment

Hardware Interfaces

  • Both Mac and Windows operating systems through their default web browser
  • iPhone
  • Android
  • Non-Functional Requirements

Performance Requirements

  • The application should load and be usable within 3 seconds
  • The application should update the interface on interaction within 2 seconds
  • The database should be normalized to prevent redundant data and improve performance
  • The database should be distributed to prevent outages

Safety Requirements

  • Databases should use sharding to be redundant to prevent loss of data.
  • Backups of the databases should be done hourly and be kept for one week.

Security Requirements

  • Any keys used for the REST API should be stored securely.
  • Only the REST API should be able to connect to the databases.
  • Databases should be behind a firewall.

Software Quality Attributes

  • Availability: Because this application is critical to business communication, we will have a goal of four nines(99.99%) availability.
  • Correctness: The application should never allow anyone to read messages or discussions not intended for that person.
  • Maintainability: The application should use continuous integration so that features and bug fixes can be deployed quickly without downtime.
  • Usability: The interface should be easy to learn without a tutorial and allow users to accomplish their goals without errors.

Summary

An SRS document is a necessary part of completing a software development project. It is the roadmap that gives direction to everyone involved in the project, so the final product meets the user’s needs.

Without a complete SRS document in place before you start a project, it will be hard to tell when a project is finished and could sidetrack development into creating unintended features. An SRS document gives you the ability to estimate a project accurately and assign tasks efficiently.

Creating an SRS document can be a time-consuming, meticulous process. Fortunately, the team at Relevant has helped over 200 companies create SRS documents and launch new products. We are ready to help with your next software project, just drop us a line.

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Written by
Andrew Burak
CEO at Relevant
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