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How to Write a Software Requirement Specification (SRS)

What’s the SRS?

The SRS is a document that describes the detailed requirements in how the software should function to meet the business and user needs. It is only one of many documents to enable developing a working software, but without being properly documented, it’ll cause bad consequences on the project results.

Why’s the SRS important?

The SRS is an essential document for all development activities from the initiation to the completion of the project because it reflects the most relevant information that the software development team needs to understand and implement the project. The more precise and detailed the requirements, the easier it will be for developers to implement their tasks. An effective SRS will help:

  • provide necessary information to accurately estimate the project costs, risks, and delivery timeline
  • give the team a clear roadmap to follow and achieve project objectives
  • ensure the information transparency across teams and parties
  • serve as a source of information for user acceptance testing
  • build a stable foundation for future customization and enhancement

5 Steps to create a good SRS

1. Start with an outline

As always, it’s important to make your document structured and focused. This will help your outsourcing development team avoid unnecessary effort in reading project requirements back and forth. As a result, it will reduce the risk of missing information across teams. You should also ensure the three main parts of the SRS, including introduction, overall description, and detailed features and requirements to create a rigorous outsourcing software document

Take a look at an outline example here:

  • Introduction:
    • Project purpose
    • Project scope
    • Glossary and reference
  • Overall Description:
    • User needs
    • Assumptions and dependencies
  • Detailed Features and Requirements:
    • Functional requirements
    • Non-functional requirements
    • External interface requirements

2. Clarify project overview

Starting the SRS with a clear introduction to describe the project’s purpose and give readers an overview of the project’s big picture. The introduction should cover the following contents:

  • project purpose: what’s the project built for? Answer this question to help the readers understand the aims and objectives of the project.
  • project scope: what’re the business goals? What values does the project deliver? Find the answers to these questions to make clear the project sophistication.
  • glossary and reference: explain terms and acronyms used in the document. Show your reference sources to readers to consolidate the transmitted information.

3. Understand users and project risks

All developing effort is to ensure that the project is completed and meet the user expectation. To achieve this success, you need to pay enough attention to analyze:

  • user needs: define your software’s end-users and how they use it. Correctly understanding the user's needs will give you a clear direction on how your software should be built.
  • assumptions and dependencies: think of assumptions and dependencies that might impact on fulfilling the requirements outlined in your SRS. And take note of external factors, for example, software components reused from another project. This is to prepare for any upcoming challenges in the project implementation and reduce the risk of project failure.

4. Detail the project requirements

Clear requirements can be considered as keys to the project deliverables in general and the project’s success in particular. The more specific requirements, the easier it will be for developers to plan and implement the project. Requirements are various but mainly divided into functional requirements, non-functional requirements, and external interface requirements.  Each type of requirements needs to be specified differently:

  • Functional requirements describe what the software will do and define how it will function to meet user expectations. You should also mention the acceptance criteria for these functional requirements to determine if a function is completed and performs as expected. 
  • Non-functional requirements include usability, performance, software quality, security, and so on. They can be seen as extensions that help describe how the software will perform.
  • External interface requirements are types of functional requirements. These interfaces include user, software, hardware, system, communication interfaces, etc.

5. Get the SRS approvals

To ensure the SRS’s accuracy and objectivity and the mutual agreements in how the software should run, the key stakeholders should be involved to approve the SRS. By doing this, you can reduce the risk of wasting time, effort, and money in future unnecessary changes.

Additional writing rules

Writing the SRS or any type of document requires you to follow some rules and recommendations. In regarding this, we recommend you to:

  • allocate enough time for the SRS outline
  • keep information precise and clear
  • avoid ambiguity
  • focus on the most difficult tasks
  • keep the document up-to-date and systematically update the changes 
  • make sure the language used in the SRS if you’re working with an outsourcing development team

Final thoughts

The SRS is important because it gives you a source of information where you can easily manage requirements throughout the outsourcing software development process. In this article, we aim to help you get the basic ideas of the SRS’s structure, and hopefully, we did it. For more best practices, you might want to explore in the next article about turning your business ideas to the SRS. Thank you for reading!


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