Re: Technical Report on Capability Classes

Hi Mark,

Very well written overall.  A few comments:

o Terminology: you use "content specialisation" but the DI Principles document 
uses "content adaptation".

o It seems to me that capability classes is a useful abstraction for delivery 
systems that use XSLT, but I'm not sure that this abstraction should place any 
additional requirements on CC/PP, UAProf, or new vocabularies. The XSL 
conditional expression limitation of certain UAProf datatypes seems to be merely 
a result of XSL's limitations, not the datatypes themselves.  Isn't it possible 
for an alternate content adaptation mechanism, e.g. JSP, to handle UAProf's 
dimension datatypes and version numbers more easily?  In my opinion, XML makes 
for a poor programming language, and XSL is therefore difficult to use for 
anything beyond simple transformations.

o I gather from section 5 that you're suggesting that capability classes should 
be considered in developing new CC/PP vocabularies.  I think CC/PP vocabularies 
should be constrained to dealing with describing "what" consitutes the delivery 
context (it's form), rather than infringing on the realm of "how" to deal with a 
particular delivery context (it's function). Granted, incompatible processing of 
delivery context information is bad, and therefore the semantics behind delivery 
context attributes should be clear.  But I think the line should be drawn at 
implying how the attributes should be handled by specifying what the attributes 
mean, rather than specifying a mechanism for handling the attributes.

o I'm not sure you've mentioned the case where the same set of XSLs are reused 
for all or a large subset of a site's XML content.  In such a case, the XSLs are 
related to delivery contexts and the XMLs are mostly independent of delivery 
context.  This often necessitates some common interface or agreement between the 
XML and XSL authors.  In this scenario, it would seem that capability classes 
would need to permeate throughout the XML and XSL authoring processes.

Thanks,
Luu

Butler, Mark wrote:

> Hi,
> 
> A new technical report is available from my web page. The mechanism proposed
> (capability classes) have some similarities with document profiles and media
> queries.
> 
> Using capability classes to classify and match CC/PP and UAProf profiles
> HP Labs Technical Report 2002-89
> http://www-uk.hpl.hp.com/people/marbut/capClass.htm
> 
> ABSTRACT
> In order for a web server to provide optimised content to different client
> devices it requires a description of the capabilities of the client known as
> the delivery context. In previous work we demonstrated DELI, an open-source
> library that allows Java servlets to resolve HTTP requests containing
> delivery context information in CC/PP or UAProf formats. Subsequently DELI
> has been incorporated into the Apache Cocoon XML publishing framework in
> order to demonstrate how delivery context information can be used in
> conjunction with content transformation via XSLT. During this work, it was
> found that it is cumbersome to match this information using constraints
> written in XPath. Furthermore there is no easy method of abstraction so that
> common sets of constraints may be reused in multiple stylesheets. This
> report describes an alternative mechanism for delivery context matching
> called capability classes. This report outlines how to implement capability
> classes and how they may be applied to various content specialisation
> techniques such as content transformation, negotiation or generation. It
> also compares and contrasts capability classes with device classes and media
> queries. 
> 
> Mark H. Butler, PhD
> Research Scientist                HP Labs Bristol
> mark-h_butler@hp.com
> Internet: http://www-uk.hpl.hp.com/people/marbut/
> 
>

Received on Monday, 22 April 2002 15:33:50 UTC