You understand the importance of clear, effective functional requirements when it comes to delivering a project on time and within budget. But even experienced professionals can struggle to create requirements that are comprehensive, testable, and implementation-neutral.

In this blog post, we’ll dive into the 7 most important tactics for writing better functional requirements that ensure project success.

After this short 7-minute read, you will be equipped with the tools you need to write infallible requirements that are clear, concise, and effective.

1. Be consistent with imperatives

The use of imperatives in requirements is a debated topic. Most functional requirement writers use “shall” as a binding provision, “should” or “may” for non-binding provisions, and “will” for declarations of purpose.

Some use “must” to express constraints and non-functional requirements.

It’s important to agree on the usage of these terms within an organization and document it in the requirements document template. In general, use one provision or declaration of purpose consistently for each requirement.

Our requirements writing software, QVscribe, detects improper imperative usage and will quickly help your team write correct declarations of purpose:

Unclear or inconsistent application of imperatives is often the cause of functional failures. Which can ultimately result in rework and lowering a project’s ROI.

2. Use identifiers to your advantage

Many requirements documents lack a comprehensive requirement identification system. Tagging each requirement with a Project Unique Identifier (PUI) improves traceability and simplifies referencing.

This becomes especially important as your team’s requirements repository grows.

Standards like IEEE/EIA 12207 often require PUIs for contract-purchased systems. Without PUIs, traceability becomes difficult, and referencing requirements within the document is harder.

The example requirements below illustrate the easy referencing and traceability that PUIs provide.

Requirements example:

• 3.5.2.4 The system shall have a login feature that requires a unique username and password for each user.
• 3.5.2.5 The system shall have a search function that allows users to search for specific products using keywords, and returns a list of matching products within 1 second.

3. Avoid using weak words

Weak words, also known as subjective, vague, or ambiguous words, are those that don’t have concrete or quantitative meaning and are subject to interpretation.

Effective requirements are free of such words and should be defined in precise, measurable terms. Avoid specifying that a system or feature will be intuitive, reliable, or compatible. Instead, define it.

Weak words are often easy to miss, which is why we’ve designed QVscribe to detect them during its quality analysis:

Here are a few examples of common weak words to avoid:

• Efficient
• Powerful
• Fast
• Easy
• Effective
• Reliable
• Compatible
• Normal
• User-friendly
• Few
• Most
• Quickly
• Timely
• Strengthen
• Enhance

4. Standardize your requirements language

To reduce confusion and misinterpretation of requirements, it is important to standardize the language used in expressing them. A dedicated section at the beginning of the requirements document can be used to define how certain terms will be used and interpreted.

For example, your requirements document may define the usage of verbs such as shall, will, and should and include annotations for each requirement.

Standardizing language helps reduce conflict and confusion in interpreting requirements and saves time while writing them.

5. Write functional requirements to be implementation-neutral

“Implementation-neutral” means that requirements should not limit design choices and should be free of design details.

Writing requirements in this way allows for more efficient design, adaptability in implementation, and reduces conflicts between requirements. Requirements should focus on the system’s external behavior, rather than dictating implementation details. Constraints on implementation should be stated in non-functional requirements.

In other words, state what the system must do, not how it must do it.

6. Make sure each requirement is testable

Each requirement should have a project-unique identifier and a testable objective, as stated in MIL-STD-498 Software Requirements Specification (SRS) Data Item Description (DID).

It’s important to consider how the requirement will be verified when writing it and to specify the test scenario. The level of detail required for the requirement will vary depending on how it will be verified.

For example, early stage requirements may be tested through inspection or user testing, while late stage requirements may be verified through software testing or system integration testing. One way to ensure requirement testability is to specify a reaction time window for output events.

7. Use EARS to write concise requirements

EARS (Easy Approach to Requirements Syntax) provides proven patterns for writing specific types of requirements, such as ubiquitous, state-driven, event-driven, optional features, and unwanted behavior.

With the press of a button, QVscribe will suggest an EARS template to improve the rigor of your requirements:

Requirements writing is challenging. And when there’s so much riding on having high-quality requirements, it’s in your company’s best interest to get guidance.

That’s why we developed QVscribe.

An easy-to-use web application and plugin that detects common requirements errors in real-time.

The best part?

It integrates seamlessly with Polarion, Jama, DOORS Next, Word, Excel, and other common requirements documentation platforms. Click the button below to start driving more ROI for your next project.