An 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 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. It also lists all the features that the software must have, what problems it will solve, how it should perform, and any rules or limitations that have to be followed. It tells what to build, not how to build it.
For example, just as a builder follows a detailed blueprint to construct a house according to the owner’s needs, software developers use the SRS to develop the intended system accurately..
Purpose of an SRS
The main purpose of an SRS is to explain what the software should do in a detailed way, which helps everyone in the project, like clients, project managers, developers, testers, and designers, to understand the same thing from the beginning. The SRS lists all the features, functions, and rules of the software, so there is no confusion later at the end. It also helps the team to plan better and estimate the time and cost of the software. By following the SRS, the developers build the exact software that the client wants, and testers check if everything is working as expected.
Importance of SRS
Why use an SRS? Because it clearly explains what the software should do, which shows how important a Software Requirements Specification is for making a good product.
1. Clear Communication for Everyone
An SRS uses simple and structured language for the tech and for the business teams to understand 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. Estimate Time & 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. Manage Risk and Scope Changes
The SRS creates a line between the developer and the client because 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.
Types of Requirements in SRS
1. Functional Requirements
Functional Requirements tell the developer what the system should do, i.e., the behaviors and functions it must perform. It serves as the basis for functional testing and acceptance criteria by the user. These are the core functions that a software should perform, and these requirements are written from the user’s perspective and then used by the developer to build the software. For example, user login.
2. Non-functional Requirements
Non-functional requirements define how well the software should perform, rather than what it should do, and focus on the quality of those features, like whether the software is fast, secure, or easy to use. These requirements help make the software more reliable, efficient, and user-friendly.
3. Interface Requirements
Interface requirements define how the software system interacts with the people using the software, devices, databases, APIs, or third-party apps. They ensure that the system communicates smoothly with everything and everyone.
4. System Constraints
System constraints are the boundaries or restrictions that the software must follow during its design and development, i.e., how or within what limits it should do those things. It says that you can build your software however you like, but you must stay within these boundaries.
5. Assumptions and Dependencies
In an SRS, Assumptions and Dependencies define the external conditions that can affect the success of the project, but are not under the control of the development team. They are important to list because they help everyone to understand the risks and real-world conditions on which the project depends.
Types of Software Requirement Specifications
1. High-Level SRS
A High-Level SRS gives a detailed description of what the software system is supposed to do, not how to do it. It does not include the technical terms and is written in simple and clear language for the clients and managers. It mainly focuses on the user expectations and gives a big picture of the idea without much technical detail. It includes the scope of the project, system purpose and objectives, use case or block diagrams, and so on.
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2. Detailed SRS
A Detailed SRS breaks down the software into system requirements into smaller technical specifications and is used by the developers, testers, and designers to build the system. It focuses on how the system will perform its functions and is written in technical language with proper rules and logic. It also includes inputs, outputs, workflows, errors, data formats, etc.
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
1. 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.
2. 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.
3. 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.
4. Unambiguous: Every sentence in the SRS should have a clear meaning, like the system responds in 2 seconds, not the system responds fast.
5. 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.
6. 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.
7. 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.
8. 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.
9. Abstraction: The SRS should only describe what the system will do, and not the working of the software.
10. Testability: The requirements in the SRS should be written in such a way that they can be tested using test cases.
How to Write an SRS Document
Step 1. Define the Purpose
The SRS is started by defining why you are writing the SRS and what all 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.
There are many tools available that help you write an SRS 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.
Best Practices for Writing an Effective SRS
1. Use simple and clear language: while writing SRS, one should use plain English so that everyone can understand it.
2. Follow a Standard Structure or Template: Use a consistent format for every SRS you create. If you are new, use the proven templates to save time so that nothing important gets missed.
3. 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.
4. Avoid Ambiguity: Do not use terms like user-friendly, fast, better, or efficient. Be precise and define the terms clearly, like adding definitions to explain technical terms.
5. Include Visuals: Use diagrams and flowcharts to explain the idea of the software you are building, which helps non-technical persons to understand the SRS better.
6. Update the SRS: When things or functionality in the software are updated, also change the SRS, use tools like Google Docs to manage the changes effectively.
7. Review and Get Approval Early: As soon as the SRS is ready, share it with all the key persons as soon as possible to get feedback and get it signed.
8. 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.
Alternatives to an SRS
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.
Traceability and Its Types in SRS
In SRS, 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.
Real-World Examples of SRS
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 |
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.