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Re: BIG ISSUE -- re Delivery Units

From: Jason White <jasonw@ariel.its.unimelb.edu.au>
Date: Thu, 9 Feb 2006 18:30:32 +1100
To: w3c-wai-gl@w3.org
Message-ID: <20060209073032.GA6640@jdc>

On Wed, Feb 08, 2006 at 03:23:45PM -0600, Gregg Vanderheiden wrote:
> Web Unit (e.g. Page)
>     A collection of information, consisting of one or more resources,
> intended to be rendered together, and identified by a single Uniform
> Resource Identifier (URLs etc.).     
Amend the end of the sentence as follows "single Uniform Resource Identifier

I raised a number of problems with the definition of "delivery unit" in public
comments relative to the November 2005 working draft.
I think this latest definition by Gregg and John addresses many of those
comments but would need to check in detail to confirm this.

A few remarks that come immediately to mind:

1. The proposal can be read as implying that the URI identifies the entire
collection of resources. However, I thought it was part of the definition of a
URI that it refers to exactly one resource only.

Maybe the definition should be something along these lines:

"A collection of Web resources intended to be rendred together. A Web unit
consists of one primary resource and may include one or more secondary
resources. To identify a Web unit it is sufficient, for purposes of these
guidelines, to specify the URI of its primary resource.

Note: the primary resource is typically the first component of the Web unit
retrieved by a user agent for the purpose of rendering the Web unit."

2. A further question relates to how this proposal, with or without my
clarifications, affects resources that refer to alternative forms of content.

Suppose I write an XHTML document containing three nested OBJECT elements: the
outermost OBJECT refers to an animation; inside this is a second OBJECT element
referring to an image, and nested within this a third OBJECT element
containing a hypertext link to a detailed description.

The animation and the image are not intended to be "rendered together",
because they are alternatives to each other. Since the description is referred
to via a hypertext link, I suppose one could say that it isn't intended to be
rendered with the XHTML document, so it isn't part of the same WEb unit. I'm
not sure whether that's a problem for conformance purposes; it might mean that
the entity claiming conformance has to be careful to ensure that both the
XHTML document and the description are within the scope of the claim. This
would require a URI pattern or the specification of both URI's in the
conformance claim.

That the definition can't tell us whether either or both of the animation and
the image should be counted as part of the Web unit could be a problem,
however. (Suppose e.g., that one of them violates guideline 2.3).

It might be necessary to say something similar to the following.

A WEb unit consists of:

1. A primary resource.

2. All resources intended to be rendered, either collectively or in any
combination, with the primary resource.

I hope these comments are helpful.
Received on Thursday, 9 February 2006 07:30:46 UTC

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