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   RE: [xml-dev] theories of media languages and error handling

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It's exactly this kind of thinking that led XML Schema to the position that
validation failures are not fatal, they simply cause parts of the document
to be marked as invalid. A position which (in the interests of avoiding
excessive complexity) the schema-aware XSLT and XQuery specs have not
followed through.

Michael Kay

> -----Original Message-----
> From: Bryan Rasmussen [mailto:bry@itnisk.com] 
> Sent: 26 July 2005 15:08
> To: xml-dev@lists.xml.org
> Subject: [xml-dev] theories of media languages and error handling
> There is an assumption one often encounters in 
> implementations for media (as a
> reference media I will focus on hypermedia in the modern 
> browser), this
> assumption is opposition to a general assumption for 
> validation of data for
> media, the media implementation assumption could be put as follows:
>  The absence of an object does not cause the failure of the 
> whole. This means
> that as a general rule if I refer to some object that the 
> browser cannot find
> the browser is not designed to fail, the browser assumes that 
> other objects
> that
> it can find are still useful to the user and do not present a 
> faulty instance
> to
> the user (sometimes of course the browser does fail but such 
> failures at
> missing
> components seem always to be due to bugs in the browser and 
> not required
> presence)
> As an example of this assumption -  a reference to an image 
> that the browser
> cannot resolve, this is generally the same behavior in printing etc.
> I am in total aggreement with this assumption. 
> The assumption for validation of data for media is often as follows:
> strict requirements for structure prevents failures in your 
> media presentation.
> But of course that someone has put in an element referring to 
> an image does not
> mean the image is placed in the page. 
> In a way we can define the components of a media instance as 
> being loosely
> coupled. How though has it come to pass that this is so? Is 
> there any theory out
> there or do people have theories? I suppose the pedestrian 
> reason is that media
> itself is dataless and any media format must allow decoupling 
> of individual
> media elements because we cannot know what their meaning is 
> without the data
> context. so that if one had a true xml browser that was 
> semantically aware we
> would be able to crash whenever a document without a required 
> image was
> enquired. 
> I am of course aware of the oodles of theory on strict 
> validation of document
> structures and so forth and why failure when data standards 
> are not held to is
> good. I am however sometimes worried that this kind of 
> strictness is only proper
> in some very few instances.  
> -- 
> Bryan Rasmussen
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