Which IREB validation quality criterion doesn't belong to specification content?

Title: Why Understandability isn’t a Validation Criterion in IREB’s Requirement Quality

Let’s talk about how we judge the quality of a requirements specification. If you’ve ever sat with a long document that tries to describe what a software system should do, you know there are a lot of moving parts. Some parts matter for testing, some matter for design, and some matter for the people who will read the document. In the world of IREB, there’s a special way this is framed. There are three validation criteria you’ll hear about most often: verifiability, necessity, and completeness of the document. There’s a common misconception floating around, though: understandability. Is it a validation criterion? The short answer is no. And that distinction matters.

Let me start by laying out the three criteria that do sit squarely in IREB’s arena.

Verifiability: can we test it?

Think of verifiability as the “testability lever.” A requirement should be written so that you can verify, or confirm, that it’s met. If a requirement says, “The system shall respond within two seconds under normal load,” you can design a test, measure response time, and check whether the goal is achieved. Verifiability is about measurability. If you can’t measure it, you probably can’t prove it’s satisfied. That’s not a moral judgment; it’s a design and quality check. Good verifiability reduces ambiguity and makes the later steps—testing, validation, and acceptance—clearer and more reliable.

Necessity: is it truly needed?

Necessity asks a hard question: does this requirement deliver value, or is it a nice-to-have add-on? It’s tempting to pile in every feature you supposedly “might want someday,” but that’s a trap. When you challenge each requirement for necessity, you keep the scope honest. Is there a stakeholder who will benefit from it? Will it reduce risk, save time, or increase revenue? If the answer is no, the requirement probably doesn’t belong in the specification. Necessity helps teams avoid feature bloat and keeps the focus on what truly matters.

Completeness of the document: are we covering all the bases?

Completeness means the specification should not leave critical gaps. It should define the boundaries, the interfaces, and the behavior that a system must exhibit under a range of conditions. A complete document minimizes interpretation ambiguity. It helps architects, developers, testers, and business stakeholders stay aligned because everyone is working from a shared, explicit picture. Completeness is the umbrella that keeps important details from slipping through the cracks.

Now, what about understandability? Here’s the thing: it’s important, but it isn’t one of the IREB-validation criteria. Understandability is about readability and how easily people can grasp what is written. It matters a lot for communication; if a document is riddled with vague terms, unclear abbreviations, or inconsistent language, stakeholders will struggle to follow along. And when people struggle to understand, misinterpretations creep in. So, while understandability is a critical quality attribute, it isn’t classified as a validation criterion in the IREB framework. It sits in a separate lane—readability, clarity, and the way the message lands—rather than in the set that’s used to judge whether the specification can be verified, is necessary, and is complete.

A simple way to see the distinction

Imagine you’re reading a requirement: “The system shall provide a search function.” If the document is lacking verifiability, you might not know how to test it. If it’s lacking necessity, you might wonder why this search feature is needed for the business. If it’s lacking completeness, you might wonder about performance, security, or how the search handles edge cases. Now, if the wording is hard to understand, you’ll waste time decoding what it means, which slows down everyone. That last problem is crucial for readers, but it’s not the same as a verifiable, necessary, or complete statement according to IREB’s validation framework.

A quick example to anchor the idea

Let’s walk through a tiny, concrete example. Suppose a requirement states: “The mobile app shall allow users to search products.” Think of a few things you’d need for verification: Can you trigger the search from the UI? Is there a response time target? Are the search results shown in a specific order? For necessity, you’d ask: Is a product search essential for this app’s value proposition, or could users navigate by category? For completeness, you’d want to know what happens if the search yields no results, how errors are presented, how results are paginated, and what metadata is included with results. Now, imagine the same line is written as: “The app should enable product query.” That sentence becomes a readability challenge. It doesn’t automatically become verifiable, necessary, or complete. It’s readable, yes, but you still need precise, testable, and exhaustive content to satisfy the IREB criteria.

Where the confusion often shows up

It’s easy to conflate readability with quality. After all, a well-written sentence feels better to read than a clunky one. But the IREB framework doesn’t treat readability as a criterion for validating the technical quality of a requirement. Readability improves collaboration and reduces misinterpretation, which is why we care about it, but it sits outside the triad that determines whether a requirement is sound from a verification and validation perspective. If you see a checklist that labels understandability as a validation criterion, that’s a signal to pause and rethink the framing. The real validation criteria are all about what you can prove, test, justify, and confirm.

Bringing it together in real-life work

So how does this play out in daily work? Here are practical takeaways you can apply when drafting or reviewing specification content:

• Build for testability first. If you can’t define a test, measurement, or observable condition for a requirement, revisit the wording. Add concrete acceptance criteria, metrics, or scenarios.

• Justify each requirement. For any item, sketch a brief rationale: what business need it serves, what problem it solves, or what risk it mitigates. If there’s no solid justification, consider removing or reframing it.

• Map out completeness. Create a lightweight traceability approach. Ensure each requirement has identified inputs, outputs, interfaces, and constraints. Think about edge cases, non-functional aspects, and dependencies.

• Improve readability, but separately. Use plain language, consistent terminology, and clear definitions. Add examples or diagrams to make intent obvious. This improves collaboration and reduces back-and-forth, even though it isn’t the formal validation criterion itself.

• Read with different lenses. Have a stakeholder from a technical, business, and user perspective review the document. You’ll catch issues a single vantage point might miss.

A few digressions that still connect back

You’ll notice I’ve sprinkled in some real-world flavor. That’s deliberate. Requirements work isn’t a sterile, one-size-fits-all exercise. It’s a conversation among people who bring different priorities to the table. The best specs emerge when you balance precision with clarity, when you honor the need to prove things work while also recognizing the value of simple, unambiguous language.

Another thread worth following is the role of constraints. Some constraints force us to be creative about verifiability. If you’re limited to certain testing environments, you’ll craft requirements that still allow objective measurement. If stakeholders push for speed, you’ll emphasize what must be verified to demonstrate real business value. Constraints don’t weaken the framework; they often sharpen it by forcing you to articulate exactly what matters.

The bottom line

To answer the original question clearly: Understandability is not a validation quality criterion for specification content in the IREB framework. Verifiability, necessity, and completeness are the pillars that enable someone to test, justify, and fully cover the scope of a system’s requirements. Understandability remains vitally important as a communication quality, but it sits in a separate category — a companion skill that makes the other three easier to apply, not a substitute for them.

If you’re looking to strengthen your own specifications, start by prioritizing verifiability, necessity, and completeness. Then, polish the language so readers don’t stumble over the meaning. This combination keeps the document robust and readable, and it helps everyone involved stay aligned without spending extra cycles on guesswork.

One final thought

As you review a spec, ask yourself: Can I verify this? Is it necessary? Is the document complete in describing the behavior, interfaces, and constraints? If the answers are yes, you’re on solid ground. If any answer feels shaky, take a step back and tighten the wording, add a testable criterion, and fill any gaps. And remember: readability matters, but it’s the trio of verifiability, necessity, and completeness that really anchors the quality of the specification in the IREB universe.

If you’re curious to keep this thread going, think of a requirement you’ve seen recently. How would you reframe it to improve verifiability? What would you add to ensure completeness? And what small language tweaks could make it easier for every stakeholder to understand, without changing the meaning? Those are the kinds of questions that keep documentation honest, practical, and human at the same time.