A software requirements specification (SRS) serves as the foundation for any successful software project. It clearly defines the expected functionality of the software and ensures that all stakeholders remain aligned. This avoids confusion, mistakes, and delays. Whether it is a small app or a big system, an SRS gives a clear plan and helps turn your idea into a working product. It also builds trust with stakeholders by showing that the project is well thought out and professionally managed.
In this article, we will learn about the SRS in detail, with real-world examples.
Table of Contents:
What is Software Requirements Specification (SRS)?
A Software Requirements Specification (SRS) in Software Engineering is a plan or blueprint that explains the main purpose of the software, i.e., what the software should do, how it should perform, and the constraints it must follow. It also lists all the features that the software must have and what problems it will solve. It tells what to build, but not how to build it, and hence, serves as a guide to developers, testers, and stakeholders. In software projects, the SRS plays a critical role by ensuring everyone, from clients to coders, understands the exact requirements from the start.
Whether you are a student learning software engineering or part of a real-world development team, understanding the purpose and structure of an SRS is key to delivering high-quality software.
Purpose and Importance of a Software Requirements Specification (SRS)
We all know that creating an SRS for every project, but why SRS is important? (it is keyword, so do not change) Why should a development team invest a significant amount of time in writing an SRS document?
The importance of SRS in software engineering lies in its ability to clearly define what a software system should do, ensuring that clients, developers, testers, and project managers are aligned from the start. A well-written SRS captures every feature, function, and constraint, reducing confusion and helping teams deliver exactly what is expected.
Below are the key benefits of a Software Requirements Specification and why it plays a major role in successful software projects:
1. Clear Communication for Everyone in a Software Requirements Specification (SRS)
An SRS uses simple and structured language that both technical and non-technical teams, like business teams, can understand. It clearly explains what is expected by the user, which reduces misunderstanding. It lists all the requirements step-by-step, making sure that nothing is ambiguous, so that everyone refers to the same document, ensuring alignment.
An SRS is a contract between the clients, developers, and testers that all agree on what the software will do, which helps the project to stay on track. It defines what is included in the project and what is not, and for any additions, there will be a justification, approval, and proper documentation of it.
3. Guides Development and Testing
Developers use the SRS to know what to build, and testers use it to test the test cases and ensure that all the features work as planned in the SRS. The functional and non-functional requirements in the SRS let developers and testers work efficiently.
4. Helps Estimate Time and Cost
The requirements mentioned in the SRS allow the project managers to predict how long it will take to make the software, what resources will be needed, and what it will cost. Due to this, the budgeting becomes stable, and resource allocation of the developers is based on the actual needs rather than guesswork.
5. Reduces Errors and Rework
When the requirements are written in the SRS, developers understand what to build, which avoids confusion and prevents mistakes between the developers. Because everything is planned from the beginning.
6. Supports Future Maintenance & Upgrades
Once the software is built, the SRS becomes a reference document that helps the teams in the future to understand the intent, updates, and maintenance of the software easily. For the new team members, the SRS is very helpful as it explains what the system does and why.
7. Improves Quality
As the performance needs of the software are defined initially, the SRS ensures that all the quality measures are present in the product from the beginning. Because of this, the testers know what to test, and developers can design the software keeping the characteristics in mind, such as loading time
8. Manages Risk and Scope Changes
The SRS creates a baseline for evaluating change requests, helping avoid hidden costs and unexpected delays. If any changes are requested later on, the developer can go through the SRS and see them. This change prevents the hidden cost and delay in the software.
Key Components of a Software Requirements Specification
An SRS document usually follows a standard format that ensures all necessary details are covered. Below are the common sections that you must include in your SRS:
1. Purpose
A purpose in an SRS describes why you are writing the SRS and what will be included in this document. This gives your SRS structure a simple outline, which makes it easy to read and update later.
2. Intended Audience and Intended Use
This section specifies who will read this SRS and how they will use it, because different readers (developers, stakeholders) need different types of information.
For example, the developer will need information about how the system will be built, while the tester will use it to write test cases.
3. Product Scope
This section in a software requirements specification describes what your software will do and the problems it will solve.
4. Definitions, Acronyms, and Abbreviations
This part of the software requirements specification is important to mention as it lists all terms and abbreviations used in the document to avoid confusion for readers who might not be familiar with these terms.
For example, LMS stands for Learning Management System, and UI stands for User Interface.
5. User Needs
It details the key needs of the user and how the system or the software solution proposes plans to address them.
6. Assumptions and Dependencies
This section of the software requirements specification states the assumptions you are making about resources, technologies, or user conditions, as well as dependencies the system will have.
7. Functional Requirements
In SRS, functional requirements list the specific functions the system must perform.
For example, if you are making a software requirements specification for a library management system, the functional requirement section will include the following:
- The app shall allow teachers to mark attendance.
- The app shall send daily reports to the admin.
8. Nonfunctional Requirements
This part of the SRS covers performance, usability, compatibility, and other quality criteria, which makes this section one of the most important, since this information will later decide its relevance in the market.
For example:
- The app must load within 3 seconds on 4G internet.
- The app must support Android version 10 and above.
9. External Interfaces
This section of the SRS explains how the system will interact with other systems, APIs, or hardware. For example, Integrates with the school’s SMS gateway for sending alerts.
Types of Requirements in a Software Requirements Specification (SRS)
An SRS document clearly defines different types of requirements, so that all stakeholders and developers share an understanding of what the software must do and how it must perform. Below, we have listed the various types of requirements with a simple example that are added in an SRS:
Writing Guidelines & Standards for an SRS
Now that we have gone over the various types of requirements that you must add to your SRS, let us now explore the various tips you must keep in mind to write a very good SRS. A good software requirements specification should be written in a way that leaves no room for confusion or misunderstanding.
Here are some important guidelines to follow when writing an SRS:
- Use clear and simple language: It is always best to use a simple, formal tone when writing an SRS. It would never help you if you use too many fancy words or complex jargon, since you have to write keeping the general audience in mind. If you use technical terms, define them clearly in a glossary.
- Be unambiguous: Anything you write in the SRS should not be vague or have more than one meaning, as this introduces confusion among the readers and mistakes.
- Use active voice: This might not make sense as a guideline, but using active voice makes requirements direct and easy to understand. For example, “The system shall display an error message” is clearer than “An error message shall be displayed.”
- Include measurable criteria: It is advised that you use quantitative terms instead of using vague terms like “some”, “fast”, “very much”. Instead, you could write something like, “the page must render in 3 seconds.” It is clearer and a better measure.
- Use standard keywords like “shall” or “must”: “Shall” is used for mandatory requirements, “Should” is used for recommendations, and “May” is used for optional features.
- Focus on What, Not How: The SRS should define what the software should do, not how it should do it. Also, do not specify the technology you are using.
- Ensure All Requirements Are Traceable: Every requirement in SRS should be traceable to its source, test case, and code module, like using unique IDs like REQ-001, REQ-002 to point to each requirement.
If you are still confused about the guidelines, there are some standards you can follow to write a perfect SRS:
- IEEE 830: Provides a structured format for writing requirements, covering sections like purpose, scope, functional requirements, and non-functional requirements.
- ISO/IEC/IEEE 29148: Offers guidelines for the complete requirements engineering process, including writing, reviewing, and maintaining requirements.
How to Write an SRS Document
At this point in the article, you are familiar with the key components of the SRS, the types of requirements to add, and the guidelines and standards to write a good SRS. In this section, we will consolidate all the knowledge that we have learnt till now and discuss how to write a mock software requirements specification step by step.
Step 1. Define the Purpose
The SRS is started by defining why you are writing the SRS and what things will be included in this document. A simple outline gives your SRS structure, which makes it easy to read and update later.
a. Intended Audience and Intended Use
In this, you define who will read this SRS and how they will use it, because different readers need different types of information. For example, the developer will need the information about how the system will be built, and the tester will use it to write the test cases.
b. Product Scope
In this, you define what your software will do and what types of problems it will solve.
c. Definitions and Acronyms
In this section, there is a list of all the definitions that are used in the software to avoid confusion. For example, LMS stands for Learning Management System, and UI stands for User Interface.
Step 2. Describe What You Will Build
In this step, you will describe what you will be building and what your system will include, which helps the influencers to understand the big picture of the product.
a. User Needs
In this section, the key needs of the user and how the system will solve them are kept in mind.
b. Assumptions and Dependencies
In this, you write the things that you will assume and will be available in place for the system to work, and what the system will depend on.
Step 3. Detail Your Specific Requirements
In this step, you should write down all the requirements of the user that are necessary to build a software system. Requirements like functional, non-functional, system requirements, and interface requirements should be included that are as defined above.
Step 4. Deliver for Approval
Once the SRS is complete, it should be reviewed and approved by all key people, i.e., by clients, managers, and tech leads, before development of the software begins. Upon approval, the development team will begin the implementation of the software based on the requirements that are mentioned in the SRS.
For example, below is a step-by-step procedure of the SRS of a Student Attendance App.
1. Purpose:
This document defines the requirements for a Student Attendance App.
2. Intended Users:
School teachers, admins, and students.
3. Functional Requirements:
- The app shall allow teachers to mark attendance.
- The app shall send daily reports to the admin.
4. Nonfunctional Requirements:
- The app must load within 3 seconds on 4G internet.
- The app must support Android version 10 and above.
5. Assumptions:
Teachers will have smartphones with internet access.
6. External Interfaces:
Integrates with the school's SMS gateway for sending alerts.
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Traceability and Its Types in SRS
In the software requirements specification (SRS) document, traceability is defined as the ability to track each requirement throughout the software development lifecycle, i.e., from its origin to its full build and testing. There are mainly 2 core types of traceability:
1. Forward Traceability
Forward Traceability tracks each requirement forward into design, code, and test cases to ensure it is implemented, such as a business need, stakeholder request, or use case. It ensures that each requirement is implemented in the code and tested.
2. Backward Traceability
Backward Traceability Tracks from the code or test case back to the original requirement. It ensures that everything that is built or tested is traced to the requirement. If a test case exists, the backward traceability will check that it matches an original requirement in the SRS.
There are many tools available that help you write a software requirements specification document effectively. Some of them are as follows
1. Word Processors
These are the basic tools that are used to write and format the SRS documents. For example, Microsoft Word, Google Docs, and LibreOffice Writer.
These are the specialized software tools that are used to create, manage, update, and trace the requirements throughout the project lifecycle. For example, IBM DOORS, Jama Connect, Modern Requirements4DevOps, and ReqView.
These tools help the team to manage both the SRS document and as well as the project progress. For example, Atlassian Confluence, ClickUp, and Notion.
4. SRS Templates and Document Generators
These are the pre-designed templates or online tools that help you write an SRS with the structure, i.e., with diagrams. For example, Lucidchart / Draw.io, TechTarget SRS Templates, and Asana / Trello.
They are used by the technical teams to maintain the version history of the SRS, along with the code. For example, GitHub, ReadThe Docs, etc.
Common Mistakes and Challenges
- Be specific and measurable, as using unclear terms like fast, can confuse the developers.
- Keep your main focus on what the system must do, as writing how it will be built, instead of requirements, will lead to inefficiency in the work.
- Work with stakeholders and end-users to ensure that nothing important is missed out, as leaving out key features will lead to incomplete requirements.
- Update the SRS regularly and keep a version history of it, because if the SRS becomes outdated, it will lead to conflict.
- Include edge-case test cases for each feature wherever necessary so that one knows how the system will behave in an error situation.
Characteristics of a Good SRS
A good SRS is not just a formal document that has a list of requirements; it should also have the following characteristics
- Correctness: The requirements written in the SRS should match the needs of the client, and everything written should be true and accurate; no wrong or outdated information should be present in it.
- Completeness: All the necessary details should be present in the SRS, and no important feature, condition, or behavior should be left out of it. For example, login, password reset, and email verification all should be included if required.
- Consistency: The SRS should not have any conflicting statements, and everything should match and flow logically. For example, one statement in the SRS says that only 1 user can log in at a time in the application, while the other says that multiple users can log in.
- Unambiguous: Every sentence in the SRS should have a clear meaning, like the system responds in 2 seconds, not the system responds fast.
- Ranking for Stability and Importance: Each requirement in the SRS should be marked with the priority, so that the developer can understand what is optional and what is a must, and what can be changed later.
- Modifiability: The SRS should be made in a way that it is easy to update or change, having sections and sub-sections is good. If in the future, the clients ask for an update, the writer should not write the whole SRS again.
- Design Independence: The SRS should focus on what the system should do, not on how it will do it. One should not write program details or design decisions.
- Easily Understandable: The language used in SRS should be simple, clear, and to the point, and everyone from the client to the developer should understand it.
- Abstraction: The SRS should only describe what the system will do, and not the working of the software.
- Testability: The requirements in the SRS should be written in such a way that they can be tested using test cases.
Alternatives to a Software Requirements Specification (SRS) Document
Though it is always best to have a proper SRS supporting your software or model, sometimes, due to the lack of time or fewer resources, you might not be able to write a proper SRS. In such cases, you have other documents that you can write to present with your product. These are listed below:
1. User Stories
User stories are a short and simple description of a feature that is told from the user’s point of view. It is used in small to medium projects that need frequent updates. They are the small functional requirements that can be compiled into an SRS when needed, and an SRS might include user stories as part of the requirements section.
2. Use Cases
Use Cases are a structured way to describe how a user interacts with the system to achieve a goal. It includes the Actor, Boundaries, and Relationships as its key components. Use cases are sometimes attached to an SRS to support the functional requirements.
3. Business Requirements Document (BRD)
BRD is a high-level document that explains why the software is needed from the point of business, not by the technical details. Sometimes, it is the starting point for writing the SRS, as it converts the functional needs into detailed functional and non-functional requirements.
4. Product Backlog (Agile)
Product Backlog is a list of features, bugs, and improvements of the software, which is mainly made from the business point of view.. While an SRS is a static document, a backlog is continuously updated based on sprint reviews and feedback.
Real-World Examples of SRS
A software requirements specification document (SRS) is used in many real-world use cases, some of which are discussed below.
| System Name |
Key Features |
Industry |
| Hospital Management System |
Patient registration, appointment, billing, and medical records |
Healthcare |
| Online Student Attendance System |
Teacher login, attendance, student reports, and admin dashboard |
Education |
| E-commerce Website |
Product, cart, checkout, order tracking, payment |
Online Shopping |
| Library Management System |
Book search, borrow or return, due date, fine |
Education |
| Online Banking System |
User authentication, transaction history, fund transfer, bill payments, and account management |
Banking |
Useful Resources
Conclusion
From the above article, we conclude that an SRS helps everyone in a software project to know what needs to be built. It explains the features, rules, and goals of the software so that developers, testers, and clients all stay on the same page. If an SRS is good, it saves time, reduces mistakes, and makes the development process smoother. It also helps in planning, testing, and making future changes easily. Whether the project is big or small, having a good SRS gives the team a strong foundation to build the right software the right way.
Software Requirements Specifications – FAQs
Q1. What are the different types of SRS?
The different types of SRS are High-Level SRS and Detailed SRS based on how much detail they include.
Q2. What is SRD and SRS?
SRD is Software Requirements Document, and SRS is Software Requirements Specification. SRS is often part of an SRD
Q3. What is a BRD?
BRD means Business Requirements Document, which explains what are the business needs from the software.
Q4. What are SRS documents?
SRS documents clearly describe what the software will do and how it should work.
Q5. Why is SRS called a black box?
SRS is called a black box because it focuses only on inputs and outputs, not on how the software works inside.