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RE: The two models of accessibility

From: Gerard Torenvliet <g_torenvliet@sympatico.ca>
Date: Wed, 2 Apr 2003 09:49:20 -0500
To: "'Graham Oliver'" <goliver@accease.com>, "WAI Mailing List" <w3c-wai-ig@w3.org>
Message-ID: <njeougryup6nzxr.020420030949@>

I mostly agree with what Graham says here. However, since people continue to
view 'accessibility' as meaning 'accessible to screen readers' and nothing
else, we need to become a little more nuanced in our terminology.

The idea that I've been working on lately is that both accessibility and
usability are relational terms. That is to say, a design is not accessible
(or usable) in and of itself, but only with respect to some target user or
groups of users. In other words, accessibility or usability are dependent on
the person or group of persons against whom those terms are being evaluated.

Under this conception, usability and accessibility are actually orthogonal
(but complementary).  Accessibility is a measure of how much of the data and
functionality presented by an interface that a user with certain
characteristics can access. Usability, on the other hand, is a measure of
the ease with which that data and functionality can be accessed by the same

Note that there are a few implications of this approach:

1. A system can be designed that is highly usable to a target group of
users. However, if that target group only includes those with a certain
disability, it may not be very usable at all for those who do not have that

2. A system can be designed that is highly accessible to users with a broad
set of disabilities, but that is not usable for that group. For example, any
corporation can take their web site and ensure that it complies with the
letter of Section 508. Because this is the case, with enough work, all of
the information and functions should be accessible. However, this does not
mean that they will be easy to use; in fact, to the contrary - experience
has shown that to make a web site that is accessible and easy to use cannot
easily be achieved by retrofitting an existing inaccessible site.

3. Accessibility is a limiting criterion on usability. If data and
information can't be accessed, it can't be used.

When I get sufficient encouragement, I would like to flesh these ideas out
to an article-length. Anybody on this list who wants to encourage me with a
venue to publish would be welcomed! :-)


-----Original Message-----
From: w3c-wai-ig-request@w3.org [mailto:w3c-wai-ig-request@w3.org] On Behalf
Of Graham Oliver
Sent: April 1, 2003 7:13 PM
To: 'w3c-wai-ig@w3.org'



AccEase Ltd : Making on-line information accessible
Mobile : +64 21 458 967
Email : goliver@accease.com
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Received on Wednesday, 2 April 2003 09:49:23 UTC

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