Software Requirements Documentation - Complete Guide by Erbis
Crafting a software requirement document (SRD) or software requirements specification (SRS) is integral for any software system. It's essentially the blueprint for the system, and making sure it's done well is vital.
To create an effective SRD, input from all stakeholders - such as the CEO, CTO, developers, and users - will be necessary. The document should be clear and concise in outlining all requirements of the system, including its purpose, features, and design constraints. We understand there are many variables to consider when preparing a software requirements specification - that's why we're here to walk you through how to write requirements for software products.
What is a software requirements specification and why is it important?
Software requirements specification is a document that contains a complete list of requirements for a software product. SRS outlines functional and non-functional software requirements and describes how the software will be used, what it will do, and how the users will interact with it.
A well-designed software requirements document provides a full list of product features, explains their purposes, and outlines technologies used for their implementation.
A big part of the SRS is devoted to the IT infrastructure setup. Particularly, the document specifies hardware and other equipment needed for project implementation, server capacity, database type, data transmission channels, and so on.
Another important part of the software requirements specification is outlining system performance indicators. For example, the document may highlight such points as software response time, network throughput, processing speed, memory usage, etc.
SRS is critical to all participants in the development process, including business owners, developers, marketers, and other stakeholders. It fundamentally eliminates all misunderstandings and misconceptions by providing a clear development plan and outlining the means for software implementation.
Overview of the software development process
A software development process is a holistic approach that includes the work of business analysts, developers, designers, testers, project managers, and other software development specialists. The software requirements specification development is a part of this process, which is typically implemented before the actual coding starts.
Understanding the stages of software development is critical for clients who want to stay updated about the team’s work progress. Below we outline a common software development flow and explain what happens at each stage of the project implementation.
Requirements gathering. To begin, the software development provider determines how to turn the idea into a working product. The team documents the client requirements, studies the market and competitors, and analyzes customers’ needs. For example, if a client wants to create an educational app, the requirements gathering will cover the following:
preferred platform - web or mobile
target audience - children or adults
education flow - gaming, video lectures, or live communication with a teacher
customers’ problems solved - gaining new knowledge or improving existing knowledge
difference from competitors - innovative learning approach or upgraded user experience
and more
Once the product requirements are clear, the team proceeds to the next development phase which is design implementation.
Design. At this stage, the team creates the software architecture, the user journey, and the interface design.
Software architecture defines the layout of the system and how its components will interact with each other. For example, software architecture can be monolithic or microservice. In the first case, the application is built as a single and indivisible unit; in the second case, it is broken down into a collection of smaller independent units.
User journey is the way the user interacts with your application from the moment they hear about it to the moment they exit the app. User journey is all about impression and experience. Designers must work through even the smallest details to ensure that the user gets a positive experience from interacting with your app and can quickly learn how to use it for their benefit. As a part of user journey and user experience development, designers create wireframes and prototypes to test app usability in the early stages. Wireframes and prototypes may be provided in a software requirements specification as a part of functional requirements.
Interface design is the visual representation of the user experience. It defines colors, fonts, icons, buttons, images, and other elements of the visual part of the app. Visually appealing designs are vital for successful user experience because they convey brand philosophy, tune users’ mood, and keep users engaged throughout their journey.
Development. This is when the development, testing, and debugging take place. Depending on the size of the project, this stage can take from several months to several years.
To maximize the effectiveness of the development process, the teams use various development practices and methodologies specified in a software requirements specification template.
The Agile methodology and the Scrum principle are the most common and effective software development frameworks. They break down development into sprints (usually, two weeks each), set short-term goals, and review results after each sprint. Agile and Scrum help developers prioritize tasks, efficiently allocate time between team members, and keep the client updated about the work progress. They are also well suited for managing critical situations and allow teams to change requirements on the go if needed.
Testing. Quality assurance (QA) and testing are conducted regularly throughout the development process. For better effect, the team may combine automated tools, specified in a software requirements specification document, and manual testing techniques. Automated testing is usually used to identify lower-level issues and logic-relative bugs. Manual testing is used to identify less critical issues which, however, have a significant impact on user experience.
QA engineers perform the following types of testing:
accessibility testing
acceptance testing
functional testing
non-functional testing
integration testing
load testing
performance testing
security testing
stress testing
unit testing
etc.
Experienced testers use a comprehensive testing approach that covers all possible scenarios of user behavior. This minimizes the bug rate and contributes to the development of a quality product.
Deployment. Software deployment is the process of making software applications and updates available for use by end-users. It involves preparing, configuring, and releasing software packages to various environments such as production, testing, and staging. Deployment can be automated or done manually depending on the complexity of the software and the deployment environment.
DevOps specialists play an important role in the deployment process. Their responsibilities vary across the projects, however, their typical tasks include:
adjusting continuous integration / continuous delivery (CI/CD)
setting infrastructure as code
monitoring and logging IT systems
providing DevSecOps (development, security, operations) services
managing software release process
By paying enough attention to the deployment process and specifying appropriate tools in a software requirements specification document, you can be sure that your customers will receive a glitchless product in time.
Maintenance. The work on a project does not end with software release. With time, the team develops new features and updates, fixes bugs, and provides technical support to users. Some of these activities are agreed in the software requirements specification when the project starts, while others are determined later as a part of a new stage of project development.
Types of software requirements
Top-quality software meets four types of requirements that are documented in a software requirements specification:
functional requirements
non-functional requirements
business requirements
user requirements
Functional requirements
Functional software requirements describe what a software system should do and how it should behave in specific situations. Such requirements clearly define how the system will respond to specific user actions and what outcomes it will provide.
For example, in an online store, when the user clicks the "add to cart" button, the system should add the selected product to the cart; and when they click the "pay" button, they should be redirected to the checkout page.
Functional requirements can be written in different formats:
Text descriptions. These are written explanations of how the system should work. The author adheres to a free writing style and describes the software feature in a narrative form.
Text description example:
The search feature in a hotel management app. To use the search feature, the user manually enters a search parameter and/or adjusts appropriate filters. For example, the user can enter "single room with sea view" into the input field and filter the search by price and location. Then the user clicks the "search" button and sees offers that match their search parameters.
Use cases. These are similar to text descriptions but based on a more defined structure. The typical components of use cases are:
actors – the users who are interacting with the system
system - a software program the user interacts with
success scenario – how the system should respond to users’ actions
alternative flow – how the system will behave if something goes wrong
It’s worth noting that, while there is usually one success scenario, there might be several alternative flows.
The use cases may be written in text or represented through diagrams. Below you can see an example of the use case that describes making online purchases in an e-commerce store.
Online purchase use case example
User stories. These are typically used for software systems with multiple user roles, such as administrators, marketers, economists, HRs, customers, etc. In a software requirements specification, user stories describe the software functions from the users’ perspective and provide a better understanding of what needs to be done.
User stories examples:
As a customer I want to view detailed product descriptions to decide if I will buy.
As a system administrator I need to manage users and adjust their system access.
As a marketing specialist, I want to create and manage marketing campaigns.
As an HR specialist, I want to get notified about upcoming work anniversaries.
As an economist, I need to access employees’ vacation and sick leave schedules.
Clearly defined functional requirements provide a holistic view of how the system should function and what value it should bring to the users. In a software requirements specification, functional requirements should be written in a plain language without jargon and narrow-focused terms, so that all stakeholders clearly understand them.
Non-functional requirements
Non-functional requirements describe the standards for the functioning of the software system. Unlike functional requirements, which describe what the system should do, non-functional requirements specify how the system should operate.
Non-functional requirements are a critical part of a software requirements specification. Based on non-functional requirements, the development team sets up IT infrastructure, chooses databases, cloud technologies, programming languages, and other software development tools.
Here are the non-functional requirements to list in your SRS:
Performance. This describes how quickly the software system should respond to user requests, process data, and handle high loads of traffic. Poor performance is not an option for an ambitious business as it leads to a decreased customer base and loss of profit. According to Google, an extra 500 ms in search page generation time decreases user traffic by 20%. A recent Google report also states that the page load time greatly influences customer bounce rate as shown on the infographics:
Reliability. This is the likelihood of a computer program functioning without errors for a predetermined amount of time in a specified environment. Software development teams use the following metrics in a software requirements specification to measure the system reliability:
Mean time to failure, the time interval between two successive failures
Mean time to repair, the average time to fix an error
Rate of failure occurrence, the number of failures appearing during a specific period
Probability of failure on demand, the likelihood of the system failing when a particular service is requested
Availability, the likelihood of the system being available for use at a given time
Scalability. This describes the ability of the system to handle increased data volumes and user traffic, as well as help slowing businesses to reduce IT resources in a short time. The best scalability is achieved through the usage of cloud technologies. When partnering with cloud service providers, organizations easily access server spaces, database storages, and other IT facilities for developing the deploying applications. They use such facilities on a pay-as-you-go basis and don’t spend time on setting up the on-premises infrastructure.
There are two types of scaling: vertical and horizontal.
Vertical scaling means increasing or decreasing the power of an existing cloud server, by upgrading the memory (RAM), storage, or processing power (CPU).
Horizontal scaling means increasing the number of resources, such as servers, in the existing IT infrastructure in order to balance out the workload among different machines
Security. This shows how well-protected the software is against any potential threats.
Secure software is developed under the secure software development lifecycle (SSDLC). As a part of SSDLC we, at Erbis, define the following software requirements in SRS specification.
Architecture plans. Before the development starts, the architecture plans should be rigorously checked using threat model methods, such as STRIDE, PASTA, VAST, Trike, CVSS, Attack Trees, Security Cards, and hTMM.
CI organization. Small changes to code help to quickly spot defects and take steps to solve them. That is why we usually specify that code commitment to the source code repository be done at least once a day.
Firmware reports. In a software requirements specification, we specify what automated tools will be used to analyze firmware on a specific device.
Usability. This is the ease with which the software can be utilized by users to achieve specific goals.
According to a recent Amazon report, 88% of customers would not revisit a website if they had a negative experience. This proves the great importance of app usability and the necessity to work out all possible user scenarios to ensure a smooth user journey throughout the app.
The tricky part of usability is that it is difficult to quantify.
When the software product is ready, the team can use usability testing to watch real users interacting with the system and note the bottlenecks to fix.
But what usability metrics are specified in a software requirements documentation template when the project is at the planning stage?
At Erbis, we use the following usability indicators;
Success rate - the percentage of users who managed to finish the tasks successfully
Number of errors - the number of errors that the users make while surfing the app for the first time
Number of back presses - how many times the users press back until they find the right path to the needed function.
Number of customer help accesses - how many times users contact customer support for help navigating the app.
Business requirements
Business requirements describe the business objectives that the software system should meet. Business requirements provide a high-level view of the business needs and help ensure that the software system is aligned with the overall business strategy.
Business requirements in a software requirements specification could be, for example, to:
Increase sales by 10% in the next quarter by incorporating an extra payment method with the cryptocurrency.
Reduce the order processing time by 40% by adopting automated order fulfillment tools.
Improve customer satisfaction by 20% by providing in-depth knowledge base with common questions and answers.
Ensure compliance with PCI DSS regulations by implementing a multi-factor authentication, using the “something you have, something you know, something you are” principle.
Save 15% on operating costs by combining three software programs into one corporate platform.
User requirements
User requirements describe the user expectations and needs that the software should meet. User requirements are listed based on detailed customer research and analysis. This includes the following activities:
conducting customer interviews and surveys
analyzing feedback on similar products
studying customer behavior and habits
understanding customers’ motivations
understanding customers’ barriers to make a purchase or use a service
investigating customers’ sources of influence (how customers hear about new products and brands)
etc.
User requirements in a software requirements specification could be, for example, to:
keep the progress after exiting the application and synchronize it across devices.
have an extra discount for paying online.
have in-app support that is easily accessible and fast responding.
have multiple interface languages.
allow inviting friends for mutual collaboration.
Creating a software requirements specification
Software requirements specification development becomes more efficient and less time consuming if you have a comprehensive development plan in place. At Erbis, we have 11 years of experience in software development. During this time, we have implemented many software projects and correspondingly many software requirements specifications. Here are the steps we follow to implement a detailed SRS in the shortest possible time:
Step 1: Gathering requirements
To develop a software requirements specification, it is necessary to identify the key software stakeholders and understand what stakeholders’ problems the software would solve.
The software product stakeholders are usually:
end-users
business owners
project managers
technical experts
At Erbis, we work closely with stakeholders at the initial stage of project implementation and use the following methods to gather software requirements for documentation:
Interviews. During an interview, it is important to ask open-ended and follow-up questions to get to specific situations rather than discuss general context.
Surveys. Compared to interviews, these help to cover a larger number of respondents in a shorter time and collect the necessary information at a lower cost.
Observation. We may observe users interacting with our product to understand how to improve it, or observe users interacting with a similar product and take notes on what could be done better in ours.
Brainstorming. During brainstorming sessions, we generate as many ideas as possible. Then, we pick up the best ideas and transform them into software requirements for our specification document.
Workshops. During workshop sessions, we discuss conflicting requirements and filter out requirements that are of less value for our product.
Role-play. Some software products have different types of users, such as administrators, narrow-focused specialists, and end-users. Role-play helps better understand the needs of each user group and is usually conducted after brainstorming.
Focus groups. This technique implies gathering requirements from specific user representatives and documenting them in a software requirements specification document.
The above methods of software requirements gathering are typically used when a new product is developed. However, when we work on software product modernization or extension, we also apply document analysis and interface analysis techniques.
Step 2: Writing and documenting requirements
Writing and documenting requirements in a software requirements specification requires a clear understanding of the project goals and stakeholders' needs. Once both of them are identified, the team commits them to paper.
Here are the mandatory rules that we follow when writing requirements in a software specification document:
Concise language. We make sure that the requirements are clear to all stakeholders, regardless of the level of their technical skills.
Consistent format. We usually use tables, lists, and diagrams to structure the information and make it easy-to-read.
Measurability. All requirements in a software requirements specification should be measurable and specific.
Traceability. We use a traceability matrix to map functional requirements with business and user requirements.
Prioritization. Each requirement should be prioritized according to the prioritization method developed by Dai Clegg, which distinguishes must-have, should-have, could-have, and won’t-have requirements.
Step 3: Validating and verifying requirements
Validating and verifying requirements means ensuring that all stakeholders agree with what is written in the software requirements specification.
In order to validate the requirements, we arrange a meeting with the client and the development team. Together we review the SRS document, explain how specific requirements will be implemented, and answer the client's questions. If the client wants to make any changes, we take the time to change the document and then schedule another meeting to ensure that everything has been documented correctly.
In order to verify the requirements, we work closely with technical specialists to ensure that requirements are technically feasible and can be implemented. We consider different ways of implementing specific features and review different software tools to be used. Considering the project budget, we offer the optimal solution from a price-quality perspective and approve it with the client.
Only when all stakeholders reach a common understanding regarding the software requirements in a specification document, do we proceed to development.
Components of a software requirements specification
Even though the content of an SRS is repeated across projects, there is no generally accepted form. Organizations decide how to document requirements on their own, and sometimes the lack of a software requirements specification example can be confusing.
At Erbis, we have 11+ years of experience developing software projects, and we know how important it is to pay attention to planning. Before starting a project, our software engineering team conducts a discovery phase, draws up a product concept, and documents software requirements in an SRS document. Even though we use an individual approach to each software product, the requirements specifications template helps us organize data and present information to stakeholders in a well-organized way.
Looking for an SRS template for your project or just wondering what it looks like? Feel free to download a full form using the link.
Introduction
This part of the software requirements specification outlines the following:
purpose of the document
target audience - software users
product value - how the users will benefit from using the product
scope - what works will be done as a part of project implementation
Business requirements
These describe how software will meet business objectives and goals.
User requirements
These describe how software will meet users’ expectations and needs.
Functional requirements
These describe specific features that the software will have
Non-functional requirements
These describe system facilities needed for efficient software operation.
Constraints
These describe the limitations and restrictions that affect the development of a software system. Software development constraints can be:
Technical - related to software or hardware environments. For example, if software is intended to run on a specific operating system, this is a technical constraint.
Resource - related to time, budget, or staff limitations. For example, if a client needs to release an MVP within 2 months, this is a resource constraint.
Functional - related to implementation specific features and functions. For example, if software should support online payments, this is a functional constraint.
Operational - related to specifics of software operation. For example, if the software must work in an offline mode, this is an operational constraint.
Legal - related to specific laws and regulations. For example, if the software must comply with GDPR, this is a legal constraint.
Acceptance criteria
Acceptance criteria are conditions that a software system must meet before it is considered complete. Acceptance criteria are also called ‘definitions of done’. They describe how specific features should work and what output they should provide.
Here is an example of an acceptance criterion. When the user fills out the login form and clicks the login button, the page is updated and the user sees the dashboard. The login process from the moment the user clicks the button to the moment they see the dashboard takes no more than 1 second if the Internet connection is stable.
Definitions and acronyms
This section provides explanations of terms and abbreviations used in the software requirements specification document.
Benefits of software requirements documentation
The benefits of SRS are many. Below are just a few advantages for both the client and development team:
Clear requirements
Before creating the software requirements specification document, the development team studies the client’s business, target market, and competitors. The team then chooses the software development vector, documents it in SRS, and sends it to the client for approval. The client is encouraged to ask any questions and make suggestions until they are totally satisfied with what is outlined in SRS. Only when both parties clearly understand what will be developed, and when and how it will be developed, does the development process begin.
Understanding full scope of work
Although SRS is not the same as a software development plan or roadmap, it provides an overview of all types of work that will be done on a project. This typically includes IT infrastructure setup, back-end and front-end development, adoption of cloud technologies, design implementation, and software testing and deployment. At the client’s request, the development milestones and deadlines can also be included in the SRS to provide a bigger picture of what will be done, and when it will be done.
Reduced risks
Clearly defined software specification requirements eliminate the risk of misunderstanding between stakeholders. They also allow owners to understand development costs, place them within a budget, and avoid unforeseen expenses. Software specification requirements give the client an idea of how long it will take to implement specific functionality. Thus, they don’t have unrealistic expectations and can build their business plans accordingly.
Seamless communication
SRS is the result of deep business analysis, thorough technological research, and intense economic study. It is created taking into account the client's budget, app performance expectations, and business growth plans. If the development team deviates from the defined software requirements specification template or does not show the desired results, the client can use the SRS as an argument for a constructive conversation with their software development provider and return the development process to the right track.
Better product quality
SRS is designed according to the industry standards and best practices. It ensures that the final product meets clients’ expectations and brings value to customers. Requirements documentation in software engineering aims to use the best IT technologies while staying within a defined budget. This gives a client confidence they will receive the best value for their money and have a top-notch product to shake up the target market.
Challenges in creating a software requirements specification
There are several challenges that the team may encounter when developing an SRS:
Vague requirements
Sometimes stakeholders may not be able to clearly articulate their requirements. This may lead to misunderstanding in a team and choosing the wrong vector of development. To avoid such a situation and make sure all stakeholders are on the same page, it is necessary to choose the right approach for requirements collection. In some cases, interviews and surveys are more effective, in others, observations and analyses bring better results.
Conflicting requirements
The example of conflicting requirements may be when a development team proposes using cloud technologies, while the client insists on on-premises IT infrastructure. To resolve this situation, the stakeholders should discuss the pros and cons of each approach and understand what resources will be spent on the implementation of each of them. With all that, the last word should go to the client, even if their decision seems less efficient for the team.
Misaligned expectations
These often happen when some stakeholders have insufficient technical knowledge and don’t understand the complexities of software development. Misaligned expectations may result in setting unrealistic deadlines or allocating insufficient resources for development. To prevent this, the team should clearly communicate all the pitfalls associated with development and be honest about their technical skills, available time, and other factors influencing the project implementation.
Unclear acceptance criteria
This is especially problematic on long-lasting projects where many different specialists are involved. Such projects have less flexibility to make changes, because setting a new task requires resource reallocation and leads to time losses. To avoid unexpected costs, it is better to spend time on documenting acceptance criteria in a software requirements specification rather than on redoing functionality and fixing issues in a ready product.
Poor communication
Inefficient communication leads to requirements misinterpretations and negatively affects a project's success. To avoid this, the software development provider should carefully choose project managers and other specialists responsible for communication with the client. Such specialists should have proven business negotiation experience. They should be able to hear and listen to the client as well as bring solid arguments to back up their views. It is vital to use advanced tools for communication and collaboration. Such tools help stakeholders to stay in touch, regardless of their physical location, and to receive timely updates about the progress of work.
Conclusion
Crafting software requirements is an important step in any software development project. It involves careful planning, ongoing collaboration and communication between stakeholders, and strong technical expertise of the development team.
A well-designed software requirement specification clearly defines software development tools and methods, explains budget allocation, and sets deadlines for features implementation. The document serves as a weighty argument in possible disputes and misunderstandings and lands all stakeholders on one page regarding what should be done and what resources should be used.
To implement a comprehensive software requirements document, the team should put the client’s and customers’ needs first. It should understand their current pains and problems and provide a solution that would solve those problems in the most efficient way.
The team should also take time to investigate the target market, competitors, and related products. They should work closely with potential users and a client to come up with a solution that is one step ahead of current offerings on the market.
If you want to partner with a software development team, a comprehensive software requirement specification document is the first thing you need to ask them to provide before the development starts. Only when agreement has been reached on all the requirements should you proceed to project implementation.
FAQ
A Software Requirements Specification (SRS) is a document containing a comprehensive list of the requirements for a software product. The SRS outlines both functional and non-functional software requirements, detailing how the software will be used, what actions it will carry out and how users will interact with it.
The key components of a software requirements specification document are business requirements, user requirements, functional requirements, non-functional requirements, software constraints, and acceptance criteria.
Functional software requirements describe what a software system should do, while non-functional requirements outline how the system should do it. Example of a functional requirement: when the user clicks the login button, the page is updated and the user sees the dashboard.
To gather requirements for a software product, you need to to identify key software stakeholders and understand their needs. Some of the methods used for gathering software requirements are users’ interviews, surveys, focus groups, observations, brainstorming, workshops and role-play. For projects that already have a part of their functionality developed, you can also use interface and document analysis methods.
First, you need to identify key software stakeholders and their needs. Then, categorize software requirements into functional and non-functional. Finally, use the MoSCoW method to define must-have, should-have, could-have, and won’t-have requirements.
