How to Write a Software Requirements Specification

Stfalcon.com
11 min readMay 28, 2023

The significance of the software requirements specification cannot be overstated within the realm of software development. Delving into the essence of this document, one might inquire about its nature. An SRS embodies an intricate portrayal of the software’s operation, encompassing its functionalities and burdens. It encompasses both functional and non-functional requisites, wherein use cases often find a place to illuminate the intricate dance between the user and the system.

What are Software Requirements Specifications?

A software requirements specification, commonly known as an SRS, serves as a comprehensive portrayal of the intended software system. Inspired by the Business Requirements Specification, this document outlines both functional and non-functional prerequisites, often accompanied by a series of use cases that elucidate the desired user interactions for an optimal user experience.

In the realm of software development, the SRS holds paramount importance as it establishes a foundation for agreement between customers and contractors or vendors. In market-oriented projects, these roles may be assumed by the marketing and development departments respectively. By meticulously assessing requirements before delving into specific system design stages, the software requirements specification aims to minimize the need for subsequent iterations. Furthermore, it endeavors to provide a practical framework for evaluating costs, risks, and schedules associated with the product. When employed effectively, software requirements specifications serve as a crucial safeguard against project failures.

To ensure the completeness and clarity of the developed product, the software requirements specification lists a comprehensive set of requirements. This necessitates a thorough and continuous collaboration between the developer, project team, and customer throughout the software development process. By fostering detailed interactions, a solid understanding of the project’s intricacies is achieved.

The format of the SRS document may vary, serving as one of the deliverable descriptions of contract data elements or adhering to other prescribed organizational guidelines. Typically, it is authored by a technical writer, system architect, or programmer, each bringing their unique expertise to the table.

Why Use an SRS Document?

A well-defined set of requirements plays a pivotal role in ensuring that the software development team delivers a solution that precisely aligns with the client’s needs. The software requirements specification (SRS) serves as a valuable tool in estimating project costs and delineating the project’s scope. Moreover, it provides programmers with crucial insights into the required technology stack, empowering them to strategize and organize their work effectively.

But that’s not all:

  • Designers get insight into the design through SRS documents so they can tailor the design to the use case.
  • Testers receive guidance on creating test cases that meet business needs.
  • With the SRS you can build a clear presentation for investors.
  • SRS is also important because it is a single source of information that prevents misunderstandings both between the project manager and the team and between the customer and the outsourcing company.

Software Requirements Specification vs. System Requirements Specification

When undertaking complex projects, it is common practice to distinguish between the system requirements specification and the software requirements specification. While both are occasionally referred to as SRS (Software Requirements Specification), it’s important to note that they are not interchangeable terms. The software requirements specification encompasses a broader scope than the system requirements specification.

The Software Requirements Specification (SRS) offers comprehensive descriptions and details about the intended software system. It provides an intricate overview of the specific requirements necessary for the software’s development.

On the other hand, the System Requirements Specification (SyRS) delves into profound insights regarding the requirements of a system as a whole. Its focus lies in delineating what the software should achieve and how it should function.

The IEEE 1233 standard is one of the recognized guidelines for developing system requirements. And, as noted earlier, do not forget that the concept of a system, in the general case, covers software, hardware, and people. System engineering, in turn, is an independent and no less voluminous discipline than software engineering.

A functional requirement serves as a directive, outlining the expected behavior of a system. It articulates the actions or operations that the system must undertake to fulfill user needs and expectations. Functional requirements can be likened to the user-discoverable features of a system. They should not be confused with non-functional requirements, which govern the internal workings and mechanisms of the system. Non-functional requirements focus on how the system should operate internally, rather than specifying its outward functionalities (e.g. performance, security, etc.)

Functional Requirements

Functional requirements consist of two parts: function and behavior. A function is what the system does (for example, “calculate sales tax”). The behavior is determined by how the system does it (for example, “The system should calculate the sales tax by multiplying the purchase price by the tax rate”).

Types of functional requirements

Here are the most common types of functional requirements:

  • Business rules
  • Certification Requirements
  • Reporting Requirements
  • Administrative functions
  • Authorization levels
  • Audit Tracking
  • External interfaces
  • Data management
  • Legal and Regulatory Requirements

Non-functional (NFR) requirements

Non-functional requirements elucidate the constraints and constraints associated with the system under development. These requirements do not directly impact the functionality of the application. Moreover, it is customary to categorize non-functional requirements into distinct groups, as is commonly done in practice:

  • User interface
  • Reliability
  • Security guard
  • Performance
  • Service
  • Standard
  • Sub-classification of non-functional requirements is good practice. This helps in creating a checklist of requirements that must be included in the developed system.

SRS Document Structure

You can find below the software requirement specification example document.

1. Introduction

Within this segment of the software requirements document, we elucidate the specific software application or product for which the SRS will outline its functionality.

Here, we articulate any perplexing technical terms or jargon that may arise within the SRS. It is crucial to avoid employing obscure words while defining a term. Instead, we aim to provide a comprehensive and easily comprehensible description of each term, ensuring simplicity and clarity. It is important to dedicate ample attention to this section, as thorough documentation of various aspects facilitates smoother design implementation in the future.

2. Overall Description

of the various aspects of the system’s functionality at a broad level. Each specific element of functionality will receive a more detailed description in subsequent sections below.

Additionally, it is highly recommended to include a Data Flow Diagram (DFD) diagram at this juncture. The DFD diagram serves to illustrate the overall interaction of the system, depicting the flow of data and processes involved.

Furthermore, within this section, we elucidate the operating environment required for the optimal functioning of the product. This includes specifying the operating system (OS), compiler versions, databases, servers, software, hardware, and any other essential components necessary to ensure the smooth operation of the product. Careful attention should be paid to providing accurate and comprehensive details regarding these aspects.

Description with restrictions. Such restrictions can be, for example, such things:

  • Programming language, database
  • Encoding standards
  • Communication standards
  • Restrictions that can be imposed by the business logic of the project

Here you describe the documentation needed for users of this product. Maybe it’s a book on HTML if it’s an HTML editor.

3. System Features and Requirements

We assign a unique identifier to each feature of the project, allowing us to distinguish and refer to them easily. For instance, server.html.editor could serve as an example.

System Feature: Description and Priority: In this section, we provide a comprehensive description of each feature within the product, highlighting its purpose, functionality, and execution priority. It is crucial for readers of the CRS (Customer Requirements Specification) to quickly grasp the rationale behind the inclusion of specific functionalities within the system.

System Feature: Stimulus/Response Sequences: We outline the triggers and corresponding responses associated with each feature. This includes specifying when and how a feature is activated. For instance, the HTML editor may be displayed upon the user clicking on the menu link labeled “Open HTML Editor.”

System Feature: Functional Requirements: This section entails an extensive and meticulous description of the feature’s functionality. We leave no stone unturned, elucidating how the feature operates, responds to errors, performs necessary checks, displays data, saves information, and other relevant aspects. The goal is to provide a comprehensive understanding of the feature’s behavior and functionalities.

4. External Interface Requirements

Interaction with the External Environment: We provide a detailed account of how the system interacts with the external world, including the utilization of APIs, methods to obtain specific data, and other relevant details. Subsections are dedicated to outlining the specific requirements related to software interfaces, “hardware” interfaces, communication interfaces, and more.

Non-functional Requirements: These are requirements that do not pertain to specific features but are essential for the system’s overall functionality.

Non-functional Requirements: Performance Requirements: Performance requirements outline specific limitations and expectations for system performance. For instance, the project database may need to handle 1000 requests per second. Meeting these requirements necessitates significant efforts toward optimizing the project.

Non-functional Requirements: Software Quality Attributes: In this section, we define the requirements related to code quality. This includes specifying the appropriate tests to be employed and the metrics used to assess code quality.

Non-functional Requirements: Security Requirements: Security requirements address measures necessary to ensure system security. For instance, in the case of an HTML editor that allows modifications to a website, it would be imperative to prevent the introduction of malicious code or unauthorized server access through the editor.

5. Preliminary Schedule and Budget

Initial Project Schedule: This section encompasses the preliminary stage of the project plan, outlining the necessary tasks, their interrelationships, and their respective start and end dates. The schedule provides a comprehensive overview of the project’s timeline and helps in visualizing the sequence and duration of activities.

Initial Project Budget: Within this section, we present an initial budget for the project, categorized according to cost factors. The budget delineates the anticipated expenses, including resources, materials, and other relevant costs. It aids in estimating the financial aspects of the project and allows for effective financial planning and management.

How to Write Software Requirements

Typically, customers and developers communicate using different languages. The client focuses on the system’s external behavior, envisioning what it will do and how end users will interact with it. On the other hand, programmers think about the product in terms of its internal workings and technical aspects.

To bridge this communication gap, a business analyst plays a crucial role in facilitating understanding between the two parties. They translate the client’s needs into requirements and transform those requirements into actionable tasks for developers. The initial step in this process is often the creation of a software requirements specification (SRS). Below, you will find a template for the requirements specification, serving as a framework for documenting the necessary details.

1. Create an outline based on your goals

The first step includes creating the outline for software requirements specification. You can create it by yourself or you may just use an online SRS template.

2. Define your Product’s Purpose

This section is crucial as it sets expectations that we will be implemented throughout the SRS.

Intended Audience and Intended Use

Define persons who will have access to the SRS and how they should use it. It includes developers, testers, and project managers, or also stakeholders in other departments, including sales, and marketing.

This should link to business goals.

Definitions and Acronyms

You have to define the risks of the project in SRS in software engineering. What could go wrong? How can I deal with it? Who is in charge of the risk items?

For example, if the failure of a medical device can cause injury, this is one level of risk. With the occurrence level and the severity, we can create a strategy to minimize this risk.

3. Describe Your Product

The next step is to describe the product. Is it a new type of product? Is it an extension of a product you have already created? Will this be integrated with another product? For whom is it?

User requirements examples

Describe your target audience. Understanding who are your users and the user’s needs is a crucial part of the process.

Assumptions and Dependencies

What assumption will be true? Are we assuming actual technology? Is the basis a Windows framework? You need to take assumptions to better understand when your product will fail or not operate flawlessly.

You should also note if your project is dependent on other factors. For example, are you taking a bit of software from an existing project?

4. Detail Your Specific Requirements

if you want your development team to meet the requirements in the right way, you must include all possible details.

Functional Requirements

Functional requirements are crucial to your product because they provide functionality.

You may also outline how your software can interact with other tools, which link to external interface requirements.

External Interface Requirements

External interface requirements are types of functional requirements. They are important when you work with embedded systems. They outline how your product will interact with other components.

Types of interfaces:

Nonfunctional requirements are as important as functional ones.

These include:

5. Submit for Approval

After completing the SRS, you have to get approval from key stakeholders. This requires everyone to review the last version of the document.

Why do you need a Technical Writer?

Software executives often ponder the necessity of a technical writer, questioning whether product developers can handle documentation tasks on their own. However, those who believe that a technical writer is dispensable within their organization, assuming that developers can tackle all documentation responsibilities, are mistaken.

Creating technical materials, such as software user manuals or research reports, demands a unique skill set. Acquiring the requisite knowledge and expertise associated with the technical writing profession is a time-consuming endeavor. It involves studying relevant theory and gaining practical experience, which contributes to the ability to effectively convey complex information to diverse audiences clearly and concisely. By hiring an experienced technical writer, you get the following benefits:

  • Clearer communications
  • Reduced technical support costs
  • Reduced documentation costs
  • The main job of a technical writer is to write software
  • requirements and professional writers produce documentation faster than product developers.

How an SRS Depends on Project Management Approach

Whether it’s developing new software, running a marketing campaign, or writing an SRS, project management makes it possible to succeed.

Waterfall

One effective approach to enhance the manageability of your project is to break it down into incremental steps. This concept aligns with the traditional project management method known as the waterfall model, which follows a linear structure. In many ways, this sequential progression resembles playing a computer game, where advancing to the next level necessitates completing the preceding one.

Agile

An adaptable and iterative-incremental approach to project and product management emphasizes the dynamic shaping of requirements and their successful implementation through continuous collaboration within self-organizing cross-functional teams comprising experts from diverse domains. Within this framework, numerous methodologies are derived from Agile principles, with Scrum being the most widely adopted and renowned.

Scrum

Scrum harmonizes aspects of traditional processes with the principles of agile project management, resulting in a distinctive blend of flexibility and structure.

Aligned with Agile principles, Scrum divides the project into manageable segments, known as the product backlog, which provides immediate value to the customer. Recognizing that customer requirements often evolve, the project scope that remains unfinished is reassessed and adjusted before each sprint. This iterative process involves active participation from the project team, the Scrum Master, and the Product Owner, with shared responsibility for its success.

Conclusion

Those who have experience in software projects understand the rapid accumulation and management challenges of requirements. The Software Requirements Specification (SRS) serves as a comprehensive documentation of the software product under development, ensuring alignment among all stakeholders. Thanks to modern requirements management tools, creating an SRS has become remarkably effortless, while the advantages it offers are undeniable.

Typically, the SRS is finalized and signed after the requirements development phase, which represents the initial stage in the software development process. If you would like to start a project, just contact us, a free consultation is available.

Originally published at https://stfalcon.com.

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Stfalcon.com

IT company designing custom web services and mobile apps. Our goal is to create useful and convenient software. We are the founder of the Air Alert app