How to Write a Software Requirements Specification (SRS) Document
A detailed Software Requirements Specification (sRS financials) document is key to building software that meets both business needs and user expectations. Clear, concise, and executable requirements align project teams, offer clarity on functionality, and act as a single source of truth throughout development.
Whether you're using agile, waterfall, or a hybrid approach, this guide will help you craft clear, complete, and testable requirements. We'll discuss best practices and the benefits of using a dedicated requirements management tool to create your SRS vs. using Microsoft Word. We also include an example of an SRS document created in Perforce ALM.
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What Is an SRS Document?
An SRS document acts as a guide for the development team, detailing how the software should perform and interact. It outlines the purpose, behavior, and functionality of a software application.
Think of an SRS as a blueprint or roadmap for the software you're going to build. The elements that comprise it should include:
Who Uses an SRS?
Why Use an SRS Document?
A well-constructed SRS document provides everyone involved in your software development process with clear direction. It informs vital decisions along your product’s life cycle and ensures that each requirement is met.
It takes time and careful consideration to create a proper SRS, but the effort pays back in the development phase. The better your team understands your product and its users’ needs, the less time it will take to complete.
The Benefits of Using an SRS Document
1. Create an Outline or Use an SRS Template
Your first step is to create an outline for your software requirements specification. This may be something you create yourself, or you can use an existing SRS template.
1.5 Definitions and Acronyms
2.2 Assumptions and Dependencies
3. System Features and Requirements
3.1.1 Numbered and Described
3.1.2 EARS format: "When [event], the system shall [response]")
3.1.3 Include Specification by Example or BDD format (e.g., Gherkin)
3.2.1 Performance (e.g., "95% of requests shall return in under 2 seconds")
3.2.2 Security (e.g., "Only authenticated users can access admin API")
3.2.3 Usability, Reliability, Compliance
3.3 External Interface Requirements
3.3.1 Performance Requirements
3.3.2 Safety Requirements
3.3.3 Security Requirements
3.3.4 Software Quality Attributes
3.3.5 Business Rules
4.2 Legal and Regulatory Requirements
4.3 Internationalization and Localization
4.4 Risk Management (FMEA Matrix)
5.2 Use Cases and Diagrams
5.3 To Be Determined (TBD) List
2. Define your Product’s Purpose
Start by clearly defining why the software is being built and what it aims to achieve. This introduction sets expectations that you’ll revisit throughout the SRS.
Intended Audience and Use
Define who in your organization will have access to the SRS and how they should use it. This may include developers, testers, and project managers. It could also include stakeholders in other departments, including leadership teams, sales, and marketing. Defining this now will lead to less work in the future.
Explain the broader objectives and benefits of the software. How does it align with your organization’s goals?
Clearly define all key terms, acronyms, and abbreviations used in the SRS. This will help eliminate any ambiguity and ensure that all parties easily understand the document.
If your project contains a large quantity of industry-specific or ambiguous terminology or acronyms, you may consider including a project glossary.
3. Describe What You're Building
Give a high-level perspective of the software: its users, interactions, functions, and assumptions about its environment. Questions to address include:
Describe who will use the product and how. Are they primary or secondary users? What is their role within their organization? What problem does the product solve for them?
Do you need to know about the purchaser of the product as well as the end user? If you're developing medical devices and med device software, you may also need to know the needs of the patient.
What does the software rely on to function properly (e.g., existing technologies or third-party integrations)? Take stock of these technical assumptions to better understand where your product might falter or fail. Understating and laying out these assumptions ahead of time will prevent headaches later.
Finally, you should note if your project is dependent on any external factors. For example: If you are reusing software elements from a previous project, the new project would depend on those operating correctly.
4. Detail Your Specific Requirements
For your development team to meet the requirements properly, include as much detail as possible. Consider breaking down your requirements into categories:
Functional requirements outline the software’s specific functionality, such as user authentication or data processing. These requirements benefit greatly from structured phrasing (like EARS) or format-driven clarity (like Gherkin or BDD). For example: rather than simply stating, "Users can log in," a requirement might say: "Given a valid username and password, when a user attempts to log in, then they are directed to their dashboard."
External interface requirements are specific types of functional requirements that outline how your product will interface with other components. These are especially important when working with embedded systems.
System features, like performance metrics or error handling, are a type of functional requirements that highlight what a system needs to function.
Nonfunctional requirements, which help ensure that a product will work the way users and other stakeholders expect it to, can be just as important as functional ones.
The importance of non-functional requirements may vary depending on your industry. To prove regulatory compliance, industries such as medical technology, life sciences, and automotive, must carefully track and manage detailed non-functional requirements.
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