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RE: theories of media languages and error handling

• To: "'Bryan Rasmussen'" <bry@i...>,<xml-dev@l...>
• Subject: RE: theories of media languages and error handling
• From: "Michael Kay" <mike@s...>
• Date: Tue, 26 Jul 2005 15:45:00 +0100
• In-reply-to: <1122386894.42e643ceb9f9a@h...>
• Thread-index: AcWR67A8K/GuQQE+Rc+0MRfwId3jZAABKFrg

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
http://www.saxonica.com/ 

> -----Original Message-----
> From: Bryan Rasmussen [mailto:bry@i...] 
> Sent: 26 July 2005 15:08
> To: xml-dev@l...
> Subject:  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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    • From: Bryan Rasmussen <bry@i...>

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