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Re: Violation of separation of content from presentation

From: Rhys Lewis <rhys.lewis@volantis.com>
Date: Fri, 20 May 2005 10:13:10 +0100
Message-ID: <D18551A6C7EA6241B960D4909EB75DF5023091C5@squid.volantis-uk>
To: <public-diselect-editors@w3.org>
Cc: "W3C DIWG (E-mail)" <w3c-di-wg@w3.org>

Elliotte, 

Thanks very much for your comment on the DIWG's Content Selection for Device Independence Last Call and concerning separation of content and presentation. Your comment has been logged under the id Harold-1.

DIWG has long recognised the importance of the separation of content and presentation. The group's views on the requirements for device independence are documented in http://www.w3.org/TR/acdi/. A number of the group's members have significant, practical experience of large-scale implementations of device independent authoring systems that themselves provide separation of concerns.

DIWG is engaged in creation of a number of related techniques that aid authors in creating device independent materials. The individual items are documented in our charter at http://www.w3.org/2004/05/di-charter-2004-06.html.

In particular, in the authoring space, we are pursuing work on physical layout of material, semantic enrichment, and mechanisms for aggregation and decomposition. The work is focused on creating modules that can be added to XHTML Version 2 and XForms, to enhance those specifications for situations where authors require to create materials that can be used across a variety of devices. However, the group is also engaged in work to extend CSS to support, for example, mechanisms for page layout that are independent of the page markup.

DISelect (our preferred acronym for the content selection work) forms just a part of this overall profile.

It is the group's intent that DISelect be available to authors writing in, for example, XHTML 2, but it is not the intent that such markup be restricted to that use. Consider the task of providing different versions of an image for different devices. This is a common requirement in situations where transcoding alone gives inappropriate results. In this situation, a markup that defines a set of images to be used under different conditions could be formed of a host language that includes DISelect as a module. A reference to an image from an XHTML 2 object element might be resolved by a processor that made the appropriate selection between alternative representations using DISelect. In this case, the DISelect markup would not be in the document containing the XHTML 2 markup itself. Indeed it might not even be in the same system.

In a similar example, DISelect might be used only to control the inclusion of materials from different sources, for example using XInclude. Once again, there is the possibility of a clear separation of concerns.

Sometimes, content selection is required even where the content is itself device independent and the reason for using it is not really associated with presentation but rather the semantics of the operation. A simple example is when the abstract for a news article is sent to a device rather than the full text of the article. The most convenient way to arrange this may be for there to be a separate resource for the abstract and for the article and for contnent selection to be used to determin which is sent. Again, in this example, there is no need for the selection markup to be in the same resource as either of the forms of the article.

Experience with practical implementations indicates that there is a real need for content selection to be available in a variety of ways to support authors in creation of materials that can be used on a variety of devices.

As with most things, though, such capabilities are open to misuse.

DIWG agrees with this comment to the extent that we believe it reflects a lack of clarity in some of the description.

DIWG had hoped that its work on its language profile would be sufficiently advanced to allow it to be referenced from the DISelect specification. Unfortunately, that has not proved to be the case, and the working draft of that work is not yet public. In the absence of that document, we propose to:

   1. add comments to the DISelect specification along the lines of this response to clarify the intent of the group
   2. add example(s) where DISelect is used to control use of external resources

Best wishes

Rhys Lewis, chair DIWG
Received on Friday, 20 May 2005 09:13:15 GMT

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