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RE: WCAG WG discussion of "authored unit"

From: Rotan Hanrahan <Rotan.Hanrahan@MobileAware.com>
Date: Thu, 29 Jul 2004 23:30:44 +0100
Message-ID: <D9BC812593BC2E44A803E6765FFA5E2D657D41@gpo.mobileaware.com>
To: "Wendy A Chisholm" <wendy@w3.org>, <www-di@w3.org>, <w3c-wai-gl@w3.org>
I am not fully familiar with the details of the discussions you 
have undertaken recently that led to the debate [1] on the 
definition of “authored unit”, but I am sufficiently familiar with 
the concept to (perhaps) offer some insight.
You said:
An "authored unit" includes a resource identified by a URI, 
together with any other resources directly or indirectly 
associated with it, that may be retrieved in the course of 
rendering or otherwise processing it.
This proposal echoes the general viewpoint held in DIWG. One must, 
of course, interpret this definition within the context of the 
concept of “resource”. A resource, for our purposes, is an 
identifiable entity that has at least one perceptible expression. 
Thus a piece of text would be a resource on the basis of being 
perceptible in visual form (or perhaps as synthesised speech).

However, this is a particularly narrow example. In the cases 
considered by DIWG, the concept of resource is expanded, yet still 
within the reasonable understanding of what we mean by the Web. 
Thus a better example would be “Today’s Weather Forecast”. This is 
also a resource. However, it has some interesting features:

Firstly, it is temporally dependent. The perception you obtain 
today may not be the same perception you obtain 24 hours hence. 
(Unless perhaps you are at the North Pole.)
Secondly, it may have multiple modes of perception, according to 
delivery context.

It is the second property that I will explore. If the delivery 
context mandates that the only mode of perception is through text 
(roughly assumed to be a form of “print”) then today’s weather 
should be delivered as text. Wind directions will be expressed 
textually (bearing West-North-West), as will be the form of 
precipitation (snow).

If, however, some graphical form is permitted (or preferred?) then 
directional arrows and images of fluffy white ice crystals may be 
So, “today’s weather forecast” is a resource comprising several 
other resources (text, images, sound, styles, etc.). The 
sub-resources (if you will permit me to use such a term without a 
formal definition, on the basis that it should be obvious) are 
also identifiable entities. Thus a URI can be associated with 
“today’s weather forecast” and other URIs can be associated with 
the sub-resources. Of course, referring to an individual 
sub-resource may not be meaningful, as such a reference may lose 
information when taken out of the context of the information 
provided by the other sub-resources. (Example: the image of the 
snowflake is meaningless unless considered in the context of the 
surrounding text, which may say “starting cold in the morning”, as 
opposed to “continuing cold this evening”).

Where are the “authored units” in all this? Firstly, consider the 
concept of authoring. It is necessary that someone create the text 
to describe the blizzard. Thus this text is authored. I also 
assume that some artist created the snowflake. Human expression is 
involved here. This is a traditional understanding of the 
authoring process. Yet the text author may have produced several 
versions of text describing the blizzard. There’s the one-liner 
for headlines and instant messaging devices. There’s the short 
paragraph for small screens, and there’s the twelve-verse poem 
produced while trapped indoors. Only one of these (if any) will be 
used. Some might also be used in conjunction with the snowflake 

Which brings me to another point. The image may look good in 
shades of blue and silver, but perhaps the device is limited to 
monochrome. In this case, an adaptation mechanism may 
automatically transform the image to monochrome. The artist did 
not produce the resulting image. Is this still something that was 
authored? I think so. The adaptation process is acting on behalf 
of the artist (though possibly not with the artist’s approval!). 
Thus the adapted image is also authored.

To me, and I believe this also applies to (most of) my colleagues 
in DIWG, something that is authored is something that was created 
by someone, or created by a mechanism that was in turn created by 
someone, or selected from a set of creations, or created through 
an adaptation of existing creations.

Why have I avoided the term “unit”? This has been a recurring 
problem. The idea of a unit suggests indivisibility. Yet we would 
generally think of a document comprising text and images as being 
a unit. We can then go on to talk about the authoring of the text 
independent of the authoring of the images. Thus “unit” is 
possibly a bad term. Yet the term is familiar and persists in 

So an Authored Unit is a set of one or more entities obtained 
through initial authoring (typically involving human effort), or 
processes (including adaptation) such that collectively they 
provide a perceptible expression (within the delivery context) of 
a resource (identified by a URI).
Thus the AU must be associated with a specific URI and a delivery 
context, and it may comprise several other entities, potentially 
themselves AUs. It is not necessary for the specific combinations 
of entities to be known in advance, but it should be possible to 
demonstrate or prove that any AU obtained from creations 
associated with a resource is deterministically derivable via the 
delivery context. You can then go on to impose requirements on any 
AUs so derived. For example, you can require that an image within 
the AU will not exceed the visual presentation capabilities 
indicated by the delivery context.

In that last example, it is not necessary that the author of an 
image be able to offer such guarantees, but anyone who provides an 
image transformation solution will have to offer such a guarantee 
if the presentation of the resource is to be acceptable.

The current DIWG Glossary [2] defines an Authored Unit as:

Some set of material created as a single entity by an author. 
Examples include a collection of markup, a style sheet, and a 
media resource, such as an image or audio clip.
The “set” in the definition suggests the set I mentioned earlier. 
The “single entity” alludes to the fact that the set itself can be 
referenced. The definition does not require that the members of 
the set can themselves be referenced, though the example supplied 
would suggest this may be the case.

I am sure that if your deliberations reach a superior definition 
of Authored Unit then it would likely find its way in to a 
revision of our glossary.
I wish you luck.
--- Rotan Hanrahan
Chief Innovations Architect
(Member DIWG)
[1] http://lists.w3.org/Archives/Public/w3c-wai-gl/2004JulSep/0203.html

[2] http://www.w3.org/TR/di-gloss/

	-----Original Message----- 
	From: Wendy A Chisholm [mailto:wendy@w3.org] 
	Sent: Thu 29/07/2004 20:00 
	To: www-di@w3.org 
	Subject: WCAG WG discussion of "authored unit"


	I would like to raise your awareness about a discussion in the WCAG WG 
	about the definition of "authored unit."  We plan to use the term in our 
	next public Working Draft of WCAG 2.0. 

	Thread begins at: 

	Advice and comments encouraged.  We plan to publish our next draft within 
	the next week. 


	wendy a chisholm 
	world wide web consortium 
	web accessibility initiative 

Received on Thursday, 29 July 2004 18:31:50 UTC

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