Writing Effective Software Requirements

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What are Software Requirements?

Software requirements are the lifeblood to any software development project. Poorly defined software requirements, or lack thereof, can contribute to a project being late, over budget, or failing to achieve the required software functionality. Taking the time to write well-defined software requirements with the input of all project stakeholders can be the difference between the success or failure of your software development effort.

Functional vs. Software Requirements

Often, software requirements are confused with functional and/or product requirements. Functional requirements are high-level product requirements. They describe how the product as a whole is supposed to operate. Typically, marketing stakeholders are responsible for the functional or product requirements. Marketing stakeholders define how the product needs to operate in order to meet market demand and be competitive with or surpass similar technology. Functional requirements are very important to have and are often incredibly helpful when transitioning into development. A project’s functional requirements can flow down into software requirements, helping the software engineers glean software requirements from the functional specification.

Why are Software Requirements Necessary?

Software Requirements are an essential component to both the design and development phase of any software project. When it comes to the software development lifecycle, it’s best to develop software requirements before getting into development. This will allow those responsible for development to have a clear understanding of what the project stakeholders intend to have developed in terms of software features and software functionality. The process of developing software requirements is collaborative, which can help sort out any unknown specifications amongst all project stakeholders. For a deeper look at which project stakeholders should be involved and WHY writing effective software requirements is vital for a successful software development effort, you can read our blog on “The Importance of Software Requirements”.

Creating Software Requirements

When it comes to actually writing software requirements, there are a few characteristics to keep in mind. We call them “The 4 C’s of Software Requirements.” Each requirement should be:

1. Complete. Each software requirement must be clearly defined and express a complete thought.
2. Correct. Reviewing the requirements to make sure that they are correct and do not conflict with any other requirement within the specification is imperative. In a situation when conflicting requirements are found within the same specification, how do you then know which requirement is correct? It takes additional time to figure that out, and may even require modifications to the software when executing software verification.
3. Concise. Refrain from writing vague requirements or run-ons. For example, rather than writing a paragraph per requirement, break down that paragraph into multiple requirements that are one thought each. Having software requirements written in paragraph form can leave a lot of openness for interpretation.
4. Confirmable. Software requirements must be confirmable – or in other words, testable. The software requirements developed during a project’s design phase will also come into play post-development. A software system’s test protocols will be specifically developed to ensure the software requirements are met. This means that the software requirements must be verified in testing – or during software verification.

Organizing Software Requirements

Writing the software requirements is just one component of the full software requirements specification. The way in which the specification is organized can impact the effectiveness of the document as well. Think of organizing the specification almost like a work breakdown structure – grouping individual requirements together by topic. Then, add in subtopics in an outline-type format.

Review

A poorly constructed software requirements specification can greatly contribute to a project being late, over budget, or failing to achieve the required software functionality. A well written Software Requirements specification should minimize or eliminate scope creep, meet all stakeholder requirements, and yield a high quality end-product. Make the commitment to spend the time and compose a really sound software requirements specification, reducing software development burdens and meeting your go-to market milestone!

For a deeper look at WHY writing effective software requirements is vital for a successful software development effort, you can read our blog on “The Importance of Software Requirements”.

At PSI, we’ve been writing software requirement specifications for over 40 years. If you have questions – or don’t know where to start – please contact us for assistance. We’re here to help!