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How to write a Software Requirements Specification Document

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Ottun Odunayo

November 02, 2023


An SRS document serves as a project blueprint, providing details about the entire work to be done before a project can commence. It not only provides details but also gives the entire project team a comprehensive overview and fosters seamless collaboration and communication among team members.


Prior to commencing software development, it is important to establish a defined strategy for project execution. This strategy helps developers and all project stakeholders comprehensively understand how the project will take place. Additionally, creating a Software Requirements Specification (SRS) document is a means to address and prevent potential errors during project development. 


This article will discuss Software Requirements Specification, the importance of SRS documents, and how to write a good SRS document.

Now, let's get started!


Outline

  • What is SRS?
  • Uses of SRS?
  • What is the content of a Good Software Requirement Specification (SRS) document
  • Differences between Functional Requirements and Non-functional Requirement Documents
  • How to write a Good SRS document 


What is SRS?

A software Requirement specification (SRS) is a document that describes software and how it would function. Simply defined, it describes the details of work to be done by a software development team before they can implement it. This document is prepared for a software project or an application. 


An SRS document gives users insight into what the project would look like, and developers use this to have an overview of how each team member can come together to deliver the work to be done and how best to do it. A good SRS document is a major requirement for building good software. 


Think of it this way: Imagine you want to build a house. First, an architect creates a detailed plan, showing you how the house will be structured. You review this plan and discuss any changes or specific preferences you have. Then, you work with a contractor to discuss the materials and ensure they perform their functions correctly. For instance, you want doors that function as they should.


Before moving forward, you also need to consider factors like the cost of materials and the size of your land. Once these limitations are addressed, you set a timeline for completing the house. Finally, everyone involved in the project agrees on the plan before construction begins.

In a similar way, an SRS document serves as the initial plan for a software project. It ensures that everyone understands what the software will do and how it will work before any coding or development work starts, helping to create a solid foundation for a successful project.


Uses of SRS

An SRS document serves as a project blueprint, saving significant time in the overall project development process. Though writing an SRS document may take time, it ultimately facilitates better organization and implementation of the project plan.


Additionally, an SRS document fosters effective communication and collaboration among team members and developers. It ensures that everyone is on the same page and well-informed about project details throughout its execution.


Furthermore, the SRS document is crucial in making informed decisions regarding project cost estimation, duration, and complexity. It enables customers to clearly understand the budget implications and whether they can proceed with the project. Conversely, it gives customers an impression of what to expect from the project before the development phase commences.


Content of a Good Software Requirement Specification (SRS) Document

A SRS document is not the same for every project. It depends on the size of your business, your budget, and the project's complexity. However, a good SRS document should contain the following: 


1. Introduction

The introduction contains the purpose and scope of the project, identifies the target audience, and describes how the audience intends to use your product. It also defines the terminology and acronyms used throughout the document.


2. Description 

The description follows immediately after the introduction. It describes the needs of the users and the various factors that affect the product. Additionally, it gives the product perspective on whether it depends on other software or can work independently. The section also highlights potential constraints impacting software development, encompasses all assumptions made within the SRS, and outlines any external dependencies that need consideration


3. Specific Requirements

Specific requirements are the precise information developers need before developing and designing the software. These requirements include both functional and non-functional requirements. Other requirements are interface requirements, which show how the software will engage with users and external systems, including communication interfaces, software interfaces, and hardware interfaces.


4. Appendix and Table of Contents

The document provides a summary of modifications made to the SRS document over time and a list of the sources and references used to make the document. Furthermore, it incorporates indexes and a table of contents to help users easily navigate the document when reviewing it. 


Difference between Functional and Non-functional Software Requirement Specification Document 

You might be wondering about the crucial importance of functional and non-functional requirements in shaping the outcome of a specific project. These requirements are not just mere details; they play a pivotal role in determining the success of any software project. Now, let's take a look and explore their significance!


Functional Requirements

They are requirements that define the functions that a system must perform. They are the total of all the functions, features, and requirements a software program must have to operate effectively. Users specify functional requirements and are usually very easy to define. In simple terms, functional requirements talk about what the software can do. 


For instance, consider the example of a two-factor authentication code sent to confirm a user's identity during login. This is a functional requirement within a Software Requirement Specification (SRS).


Non-Functional Requirements

Non-functional requirements are the qualities that a system must possess. They play a vital role in evaluating how well the software performs and are more concerned with user expectations than specific features. Non-functional requirements impact the overall system's performance and user experience. These requirements encompass qualities such as:

  • Reliability
  • Simplicity
  • Security
  • Usability
  • Performance
  • Availability

For example, loading a website within 3 seconds illustrates a non-functional requirement. It defines a performance criterion that users expect, specifying how quickly the website should respond.


Are you still confused about the difference between functional and non-functional SRS? If yes, let's use the example of ordering pizza to clarify further:


Functional SRS is like knowing what types of pizza are on the menu, such as barbecue chicken, margarita, or pepperoni, and understanding the available toppings. It's all about the specific options you can choose from when ordering.


On the other hand, non-functional SRS pertains to aspects like how long it will take to prepare your chosen pizza, whether there's an online ordering option for convenience, and any other factors that affect your overall pizza ordering experience. These details are about the process and qualities surrounding your pizza order rather than the specific choices.


How to Write a Good SRS Document

1. Create an Outline

The first step to writing a good SRS document is to create an outline using a template. If you prefer not to rely on a pre-made template, you have the option to create your own from scratch. This outline contains 


1. Introduction


1.1 Purpose

1.2 Intended Audience

1.3 Intended Use

1.4 Scope

1.5 Definitions and Acronyms


2. Overall Description


2.1 User Needs

2.2 Assumptions and Dependencies


3. System Features and Requirements


3.1 Functional Requirements

3.2 External Interface Requirements

3.3 System Features

3.4 Nonfunctional Requirements



The outline can include more things based on your preference. After creating an outline, what's next is to define the purpose.


2. Define the Purpose of your Software

Defining the software's purpose provides insights into its development and functionality. When articulating the software's purpose, consider the following:


a. Intended Audience and Use

Identify the audience and those who will have access to the document. Your primary audience is usually developers, testers, and designers. Recognizing your audience helps tailor the content accordingly. Regarding intended use, clarify how individuals should navigate and interpret the document, even if they lack technical expertise.


b. Scope of the product 

Discuss the features, benefits, and vision of the product. Describe how the product aligns with the business's overall goals and objectives.


c. Definitions and Terms

Include the terminology and abbreviations used within the document. Furthermore, provide clear definitions for these terms to facilitate comprehension for anyone accessing the document.


3. Give an Overview of your Product

Here, you describe what and who you're building it for. Questions frequently asked include:

  • Who is the product meant for?
  • Is the product a new one or just a refined one?
  • Can the product be used with other existing products, 

When describing these things, the following should be considered:

  1. The users' needs and their expectations. Consider their pain points, desires, and requirements.
  2. You also want to dwell on the project's assumptions and external dependencies. 


4. Describe your System Requirements and Features

Before a software project can start, defining and documenting all the necessary requirements is crucial. These requirements fall into two main categories: functional and non-functional requirements. Additionally, external interface requirements, a subset of functional requirements, are critical in determining how the software interacts with other components. These external requirements include the user's experience and the various communication channels.


5. Get Approval

After all is done, allow stakeholders (developers, testers, designers, and any other individuals with a vested interest in the project's success) to review the document. Comments made should be taken note of and implemented if necessary. Once everything is set and good to go, seek approval, and the project can officially begin once approved.


Conclusion

Creating a Software Requirement Specification (SRS) document may appear tedious, but getting a hold of it can significantly help develop the right software within the designated time frame. An effective SRS should function as a project blueprint, addressing all aspects of the project. Producing a quality SRS document necessitates productive teamwork and key attention to detail.


In essence, a well-crafted SRS document plays a vital role in establishing a solid foundation for a software development project.

 


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