RE: [xml-dev] Re: determining ID-ness in XML

[Elliotte Rusty Harold <elharo@metalab.unc.edu>]

At 4:24 PM -0600 11/5/01, Bullard, Claude L (Len) wrote:
>Isn't the point to use a means the XML processor
>isn't free to ignore per specification?  That is
>why the concept of "reliability" was introduced
>although one could say "efficiency" and mention
>the cases of XPointers and serialization.
>

No. That's not the point. It never has been. The XML processor is 
most certainly free to ignore the semantics of xml:id, just like 
today it ignores the semantics of xml:base. In fact, I would be very 
surprised if an XML processor did recognize anything special about an 
xml:id attribute. The client application that receives data from the 
XML processor would impart certain semantics to xml:id, though even 
there it would be free to ignore the standard semantics and apply 
local processing rules instead, or simply ignore the attribute 
completely, if that's what made sense to the people using the client 
application. Of course this is exactly how every other specification 
is implemented in practice today. Local client apps can always do 
whatever they need to do.

People keep getting confused with what we're really asking for 
because ID has a certain meaning in the context of XML 1.0, but none 
of that's necessary or even relevant here. We are *not* talking about 
XML 1.0 or schema ID attributes. All we're asking for is  name we can 
link to. This could be done purely within the XPointer specification 
without touching XML core. This reminds me a little of the type 
debate a month ago, so let's steal a march from that flame war and 
change the vocabulary so we stop getting confused.

I officially withdraw my request for a standard xml:id attribute for 
XML documents.

I issue a new request for a standard xml:target attribute. This would 
provide a unique name for XPointers to link to. It would have no 
necessary type. It would have no affect on validity. The documents in 
which it appears may or may not have DTDs, may or may not be valid, 
and may or may not declare this attribute with any particular type. 
Whether such a document was valid would be determined exactly 
according to the rules of XML 1.0. If xml:target (and everything else 
in the document) were properly declared the document would be valid. 
If xml:target were not properly declared, the document would not be 
valid. No parsers would change. The definition of validity would not 
change. The only necessary change would be to XPointer and other 
client specifications that needed to pay attention to this attribute. 
Everybody else can ignore it.

A few people seem to think that the xml: prefix is more special than 
it is. The only thing that's special about it is that the namespace 
doesn't have to be declared; but if that bothers you we can revise 
this. Instead of using the xml: prefix we can use the xptri prefix 
mapped to the http://www.w3.org/2001/xpointer-instance namespace URI. 
As always the prefix can change as long as the URI remains the same.

>One extends the system vocabulary precisely because
>it extends the requirement for the XML processor.
>If all you need is a convention, a PI or an
>alternative namespace are equally ignorable.
>Otherwise, we could just go on as is:  "if you
>need an ID, spec a DTD and cite it in the
>contract for the communication when using
>well-formed files.  This is only as reliable
>as your partners are diligent."
>

I'm not quite sure where you draw the line on what is and is not the 
system vocabulary. I could implement the xptri scheme in my own 
software today without stepping on anyone's toes. That's what the X 
in XML is all about. But it would probably be easier if we all agreed 
on using the same thing for the same job.
-- 

+-----------------------+------------------------+-------------------+
| Elliotte Rusty Harold | elharo@metalab.unc.edu | Writer/Programmer |
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|          The XML Bible, 2nd Edition (Hungry Minds, 2001)           |
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