How to write System Requirements Specification - blog cover

As an experienced software development company we know that writing good system requirements specification is pivotal to the success of any software project. Working with dozens of different requests from various industries we have accumulated knowledge and created a vision of how ideal SRS documentation should look like. In this article, we share our best practices for creating outstanding SRS documentation which will be both very comprehensive for the developers and protect your project from some of the challenges you and your business may face without having well-outlined system functionality and requirements to the final software.

List of the Contents

WHAT IS THE SYSTEM REQUIREMENTS SPECIFICATION

Every software has specific goals and serves particular purposes. Each goal and purpose translates a process or several processes that the software aims to solve or to automate. To deliver the right product, we should define it well from the beginning. System requirements specification or SRS frameworks development, it documents every operation and dictates how software should behave, it can be as detailed as what a button should do and should be as complete and correct as possible. The purpose of a system requirements document is to describe the behavior as well as the different functionalities of an application or software in a specific environment.

In this blog post, we are going to discuss System requirements specification or SRS and its needs. We will give some advice to help you while writing software requirements specifications, and we will enumerate some common bad practices and writing good requirements examples that you can you use as a guide. Then we will take software system requirements examples to better understand the concept. 

specifications as a way to save failing software projectFirst of all, let’s address the reason why it is essential to write a system requirements specification during the development process as documentation is its inevitable part. Writing a good system requirements specification (SRS) is important for several reasons:

  • Clarity and understanding: A well-written SRS document ensures that all stakeholders have a clear understanding of the system’s capabilities and limitations. This can help to prevent misunderstandings and reduce the likelihood of scope creep.
  • The basis for design and development: The SRS document is used as the basis for the design and development of the system. It provides the information needed to create a detailed design and to develop the system according to the requirements.
  • Communication tool: The SRS document serves as a communication tool between the various stakeholders and the development team. It can be used to ensure that everyone is on the same page and that the system is being developed according to the needs of the stakeholders.
  • Quality assurance: A good SRS document can be used as a reference for testing the system to ensure that it meets the requirements outlined in the document.
  • Maintenance: The SRS document should be kept up to date as the project progresses and should be used as a reference for future maintenance and upgrades.
  • Cost Effective: A well-written SRS document can help to reduce development time and costs by providing a clear and complete set of requirements. This can help to avoid costly changes and rework during the development process.

Therefore, a good SRS document is critical for the successful development of a system or software. It helps to ensure that the system meets the needs of the stakeholders, is developed according to the requirements, and is of high quality.

WHY SHOULD SRS BE INCLUDED IN THE SOFTWARE DEVELOPMENT PROCESS

Initially, customers or product owners work on writing system requirements specification to define the objectives of the software as well as the scope of intervention of the team that develops it. A thorough description helps the development team to implement and build software. We then use the system requirements specification to validate and check the product to ensure that it has the required features. Development should start from a specification. If somehow the delivered software doesn’t meet the requirements, the specification serves as a reference, and the development team works to meet all the described needs.

Writing technical specifications for software is then an important starting point for any development project. It involves not only the development team but also the owners and/or users. It helps the development team during the design and implementation of the product. Making sure that the specifications are complete and clear, which means that they do not lead to ambiguity, prevents spending lots of time correcting, redefining, and reimplementing the software. Moreover, early detection of problems in specification leads to effective time management since it is a lot easier to update specifications prior to any development than to update the specification and then the corresponding functionalities.

Generally, writing technical specifications for software comes after a first discussion between the development team and the product owner. Specifications serve as a reference for cost and time estimation. Since writing system requirements document aims to describe faithfully the software to develop, it makes the estimation process a lot easier and much more accurate.

Additionally, the development of an application is an evolving process; it will not always involve the same persons. Writing software requirements specifications aims to document the behavior of the software, making it easier to hand over the development from one team to another. This is why it is essential to know how to write a requirement specification.

Knowing how much time your project will require to complete will be a good start.

Read our previous article, “How to calculate man-hours for software development”, to learn how we set a timeline for our customer’s projects. Also, you can contact us in the website chat or via the form to get an expertly crafted estimation of the development duration and cost for your specific case.

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A good specification makes the product easier to update. Any change in the software requires updating the project requirement specification and inviting every party involved in the process to rethink the changes to be made.

Moreover, SRS can be used like Functional Specification Document (FSD) or Product Requirement Document (PRD). SRS includes requirements that help write Functional Specification Document and can even include FSD, SRS describes all functionalities and explains how the functionality will inside a given system as a part of a larger system or as an independent system. FSD is the software-only part of an SRS document. Indeed, an SRS may contain hardware requirements and system interaction requirements as well.

It is crucial to write a good software system requirements specification. Later in this blog post, we are going to analyze the system requirements specification document example to understand the difference between well-written and poorly-written specifications. In the following section, we are going to see how to write a system requirements document.

HOW TO WRITE SYSTEM REQUIREMENTS SPECIFICATION

In this section, we are going to learn how to write SRS document. A good system requirements document should answer the following questions:

  • What should the application or software do? Answering this question helps identify the main functionalities and the primary purpose of the software.
  • How should the software behave? It helps to understand how the app interacts with the environment where it is deployed; it also defines the hardware specification and defines the IHM: how the software interacts with the end users. The software to be described may be a whole system, but sometimes it is part of a more extensive system. It is then essential to define how this part interacts with a bigger system, and how the two systems communicate with each other. CRM system requirements specification is a good example of system requirements where it is essential to understand how the software should behave.
  • What are the requirements in terms of performance? It will, for instance, give information about the acceptable response time, how fast it should respond, and how fast it should handle problems when they occur.
  • Are there requirements or constraints that should be taken into account or respected? It aims to determine the constraints to be taken into account during the design, development, and deployment of the system.

Now that we have defined what an SRS should contain and what questions it should answer as well as how to write SRS document, let’s see how to write software requirements the different steps needed to write an SRS.

The outlines may differ from one project requirement specification to another. However, we can consider the following outline:

  • An introduction: The first step for how to write a requirement specification is to agree on what the software should do, whether we are writing a CRM system requirement specification or another system requirements specification. At this point, it is important that the development team and the product owners define and write this part together. The product owner doesn’t necessarily have the skills to write a good SRS, but the development team doesn’t know what the end users need. This is why It is important for the two parties to work closely together at this stage. In this section, it is important to put the software to build in its context. Here, we address the reason why the product needs to be built, who is going to use it, and what it should or should not do (sometimes, it is helpful and necessary to mention what we should not expect from the software). Sometimes, some terms are specific to the business, and their mention in the systems requirements document is important to understand the specification and to build the software. It is essential to define these technical terms so that the content can be understood. At the end of the introduction part, we can include a brief overview of the document to give the readers an idea of what they can expect from the system requirements document. It is also important to mention in the SRS all the documents that can be read to have a further understanding of the system, and all references should be documented as well.
  • A general description: In the description section, it is important to explain the different functionalities of the application. In this part, the hardware interfaces and user interfaces are defined. In what device do the end users expect to access the application, for instance, or what are the functionalities, how can users expect to see them in the application, what is displayed on the menus, and what are the other parts like Reports, exports, etc.?
  • Specific requirements: In this section, all the necessary details are described so that it is made easier to design the product and validate it according to requirements. Here, it is important to describe all inputs the software handle and all the outputs to better define interaction with other systems and facilitate integration. The functionalities enumerated in the previous section will be detailed here. The performance criteria need to be defined here as well. It may be tempting to leave for later some parts of the documentation that may change during the development process or at a later stage. However, it is important to thoroughly document the SRS and update the content if needed and when needed.
  • References: It may sound obvious now that we mention it, but it is important to include information about the content so that it is easier to find the information when needed.

What is the importance of requirements in software development?

Understanding the value of precise requirements also streamlines the process of writing an SRS document. You can also check the article with the detailed comparison of functional vs non-functional requirements for additional details.

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SRS BAD PRACTICES

The software requirements specification sets the foundation for the entire project. A well-written SRS not only defines what the final product should do but also how it should do it. However, creating an SRS that meets the needs of all stakeholders and sets the project up for success can be challenging. 

SRS bad practicesAn SRS is a technical document, and there are a few practices to avoid when writing a good system requirements specification. We will see these bad practices through the software system requirements specification example.

  • Incomplete dictionary: An SRS may include jargon that only people familiar with the business can understand. A requirement specification aims to give everyone involved in the development a better understanding of what the software does etc. it is important that everyone understands all the terms that are used in the system requirement document. Before using them, it is important to define them, even better have them at one place so that readers can find them quickly when needed
  • Mixing concepts: It may be tempting to throw all information we have at the same place, but that leads to poor documentation.
  • Include development instruction: It is important to separate software requirements from technical implementation. The product owners know better their needs and the development team knows better how to develop the product that meets these needs.
  • Passive action: It is important to know what to expect from the software, but it is as important to understand who is going to interact with it to have the expected result. For instance: reports are generated by clicking on a given button. It is important to know that we expect the report generation from the software, but it is also important to know who is going to click on the button to generate the report.
  • Ambiguous and incomplete documentation: Sometimes, some requirement lines may lead to several interpretations. However, it is important that they are clear and don’t lead to misunderstanding or interpretation for both documentation writers and the persons to whom the SRS is intended. Also, for each functionality or situation described in the SRS, it is important that the SRS does not present aspects that are not determined yet.

These are just some examples of bad practices in SRS, and it’s important to understand that every project is different and may have its own set of specific challenges and requirements. So, it’s important to be flexible and adaptable when developing the SRS and to be willing to make changes and improvements as needed.

THE DIFFERENCE BETWEEN THE BAD AND GOOD REQUIREMENTS SPECIFICATION DOCUMENT ON THE EXAMPLE

Now that we have defined what’s an SRS and, seen how to write software requirements, and what is generally included in one requirement specification among the most common bad practices, let’s consider simple yet useful system requirement specification document examples.

Let’s consider a system requirements example for a system managing ATM cash withdrawals. First, check out a system specification example of a poorly written specification and then see how to write good requirements.

POORLY WRITTEN SPECIFICATION

When a customer selects from the menu that he wants to withdraw money, he will be asked to choose how much money does he want to withdraw. The system is checking his account to see if his balance allows that transaction. If his balance allows the transaction, the transaction is validated. The system releases the customer’s card and delivers the cash with a receipt of the transaction. All the operations must be fast.

This system specification example seems clear. However, when we do some analysis, it presents some examples of bad practices. This specification lacks clarity, and it does not tell:

  • For the choice of the amount:
    • how the customer chooses or indicates the amount, he wants to withdraw.
    • Is there a list of choices
    • can he manually input money he wants to withdraw
    • how much is the limit he can withdraw during a single transaction
    • is there any rule for an acceptable amount a customer can withdraw
  • For the validation of the transaction: what are the rules for the validation?
  • For the money delivery: does the customer receive a receipt all the time?

WRITING GOOD SYSTEM REQUIREMENTS EXAMPLE

The previous specification can be improved as following after taking into correcting the bad practices we have identified earlier. Earlier, we have seen how to write a software specification, in this section, we are going to apply the good practices we have mentioned.

When a customer selects the menu: “Withdraw money”, he has the possibility to choose between six different amount on the screen: $10, $20, $30, $50, $100, $200, $300, or choose from the screen to input manually the amount he wants to withdraw. The amount must be multiple of one of the tickets issued by the ATM while respecting the maximum number of tickets for a transaction. Once the customer has chosen the amount, he can select the validate button to continue with the transaction or select the сancel button to cancel the transaction and get back his card. If the customer validates the amount he selected, the system validates if his balance allows him to withdraw the amount he requested and if the customer has not yet reached the maximum daily amount. The system also validates if the ATM can issue the amount: the system checks if the ATM has enough money to satisfy the customer’s need and if the amount is a multiple of delivered tickets. If the validation is OK, the system asks the customer if he wants a receipt for his transaction. If the customer wants a receipt for the transaction, the system prepares the receipt, releases the customer’s card, and delivers the money and the receipt. If the validation is OK, but the customer does not want a receipt, the system releases the customer’s card, and delivers the money. If the transaction is not validated, the ATM releases the customer’s card and displays the reason why his transaction has been denied. Every transaction should take at most three seconds.

WHO CAN BE INVOLVED IN THE PROCESS OF WRITING THE SRS?

A system requirements specification document defines the behavior and functionality of an application or software in a specific environment and serves as a blueprint for the development process. The SRS is used to clearly communicate the goals and objectives of the software to all stakeholders, including developers, project managers, and clients. It is an essential part of software development as it ensures that the final product meets the needs and expectations of the users.

To create an accurate and comprehensive SRS document, it is important to involve all relevant stakeholders in the process. This includes

  • Project Manager: The project manager is responsible for overseeing the development of the software and ensuring that the SRS document is accurate and complete. They need to be involved in the process of writing the SRS document to ensure that the project stays on schedule and within budget and to ensure that the final product meets the needs of the end users.
  • Development Team: The development team is responsible for designing and building the software. They need to be involved in the process of writing the SRS document to ensure that they understand the requirements and can design and build a product that meets those requirements. The development team should provide input on the technical feasibility of the requirements and ensure that the SRS document includes all necessary information for the development process.
  • Product Owner or/and Business Analyst: The product owner or business analyst is responsible for representing the needs and desires of the end-users. They are the main point of contact between the development team and the end users. They need to be involved in the process of writing the SRS document to ensure that the requirements are accurate and that the final product meets the needs of the end users. They should provide input on the functional requirements of the system and ensure that the SRS document includes all necessary information for the end-users.
  • Quality Assurance Team: The quality assurance team is responsible for testing the software to ensure that it meets the requirements outlined in the SRS document. They need to be involved in writing the SRS document to ensure that the requirements are testable and that the testing process is efficient and accurate. They should provide input on the non-functional requirements of the system, such as performance and security.
  • Subject Matter Experts: Subject matter experts provide technical or domain-specific knowledge and can provide valuable input on the system’s requirements. They should be involved in the process of writing the SRS document to ensure that the requirements are accurate and that the final product meets the needs of the end users.
  • Stakeholders: Stakeholders are anyone who has an interest in the project, whether they are internal or external to the organization. They can include customers, investors, and other parties using the software. They should be involved in the process to ensure that their needs and concerns are addressed.

It’s important to ensure that all stakeholders are involved in writing the SRS document to ensure that the final product meets the needs of all relevant parties and that the development process runs smoothly. This can be achieved through regular meetings and reviews and by involving all stakeholders in the process of writing, reviewing, and approving the SRS document.

Furthermore, it’s also crucial to keep in mind that the SRS should be kept updated and reviewed throughout the project’s lifecycle, as requirements can change and evolve over time. It’s important that the SRS document is updated to reflect any changes in requirements and that all stakeholders are informed of these changes.

IN CONCLUSION

A system requirements specification is a must when it comes to developing software. Some good practices lead to good documentation. Since SRS is useful for both customers and the software development team, it is essential to develop a complete and clear system requirements document, in this blog post, we have seen how to write a software specification. SRS helps the customers to define their needs with accuracy, while it helps the development team understand what the customers need in terms of development. Investing time in writing the SRS document will lead to the successful development of the software the customers need.

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Frequently asked questions

What is the system requirements specification?

A system requirements specification (SRS) is a document that outlines all the necessary information for a system or software to be developed. It typically includes functional and non-functional requirements, as well as constraints and design considerations. The SRS is used as the basis for the design, development, and testing of the system or software, and is used to ensure that all stakeholders have a clear understanding of the system's capabilities and limitations.

How to write an SRS document?

Writing a system requirements specification (SRS) document can be a complex process, but it can be broken down into several steps:

  • Identify the stakeholders

  • Define the scope of the system

  • Gather functional requirements

  • Gather non-functional requirements

  • Write the SRS document

  • Review and validation

Why is it important to set proper system requirements specification?

The properly written SRS document is critical for successfully developing a system or software. It helps to ensure that the system meets the needs of the stakeholders, is developed according to the requirements, and is of high quality.

Who needs to be involved in the process of writing the system requirements specification?

In order to create a comprehensive SRS document, it’s necessary to engage the following parties:

  • Project manager

  • Development team

  • Product owner and/or business analyst

  • Quality assurance team

  • Subject matter experts

  • Stakeholders

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