Re: Functional versus non-functional requirements for accessibility

Hi Daniel

Apologies for the lack of detail in the response as I need some clarity on what you’re asking. I assume it’s from a survey comment I left, but I can’t remember the details of what I said!

But in general, I’m referring to the distinction in software engineering between:

  1.  functional requirements—things that define what a product should do, and
  2.  non-functional requirements—constraints on the system and its development

Non-functional requirements would cover things like security requirements, response time, usability, and accessibility. [1]

For example, a system might include a functional requirement that a user can purchase a product.

And some associated non-functional requirements would be that the purchase process should be secure, accessible, and usable across a set of specified platforms and environments.

In other words, we can say that WCAG conformance is a non-functional requirement of a web product. Each of the product’s functional requirements should be implemented in a way that ensures the functionality is accessible to users with disabilities.

Does that help?

Dave

[1] https://en.wikipedia.org/wiki/Non-functional_requirement


--
David Sloan (he/him)
Principal Accessibility Engineer
Strategy and Research Lead

 [Tpgi]
TPG Interactive
www.tpgi.com<https://www.tpgi.com/>

A Vispero Company
https://vispero.com

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From: Daniel Montalvo <dmontalvo@w3.org>
Date: Wednesday, 9 June 2021 at 09:59
To: David Sloan <dsloan@tpgi.com>
Cc: public-wai-curricula@w3.org <public-wai-curricula@w3.org>
Subject: Functional versus non-functional requirements for accessibility
CAUTION: This email originated outside Vispero. Do not click links, open attachments or forward unless you recognize the sender.


Hey Dave,

As per your comment about distinguishing functional and non-functional requirements.

Currently I have capture this as follows.

[[

Topic: Establishing Requirements

Present the W3C accessibility standards. Discuss policies that apply in the students' region (if any). Explain functional and
non-functional requirements related to people with disabilities.

Learning Outcomes for Topic

Students should be able to:

* identify different non-functional accessibility requirements, for example those included in WCAG and in applicable accessibility
policies
* identify different functional requirements that relate to people with disabilities, for example:
  * appropriate contrast ratios
  * availability of content and functionality in different screen sizes and configurations
  * keyboard compatibility
  * compatibility with assistive technologies and adaptive strategies
]]

For context, see
https://deploy-preview-347--wai-curricula.netlify.app/curricula/designer-modules/understanding-and-involving-users/#topic-establish
ing-requirements

But I am a bit hesitant as to how this is going to be understood. On the one hand we could consider WCAG as non-functional (it does
not tell you how to do things) but on the other hand WCAG does have specific requirements such as contrast ratios, descriptive
labels and headings, that could be understood as functional.

Could you please expand on this a bit more? How would you better capture the difference between functional and non-functional
requirements for accessibility?

Best.

--

Daniel Montalvo

Accessibility Education and Training Specialist
W3C/WAI