Entities and XPointers

Peter Murray-Rust peter at ursus.demon.co.uk
Tue Dec 2 23:42:13 GMT 1997

At 16:35 02/12/97 -0500, David G. Durand wrote:
>On Dec 2,  5:40pm, Simon St.Laurent wrote:
>> Subject: Entities and XPointers
>> While they don't provide the actuation flexibility or many of the other
>> features of XML-Link, it may be possible to create external entities
that use
>> XPointers in the URL. Of course, this would require that either the
>> application can cope with XPointers (unlikely in this case), or that the
>> server can interpret the XPointer and return only the chunk requested.
>There's no reason that you can't do this at the server side, and a client
>was so sophisticated could interpret the URL (but, pracitcally speaking, I
>wouldn't expect many such to exist).

I am probably missing something, but it seems fairly straightforward to
extract something from another document - the question is whether it's
allowed. For example, 


could return a chunk of well-formed XML. (JUMBO is capable of the second
form at present). The question is whether

<!ENTITY chap3 "foo.xml#DESCENDANT(3,CHAP)">

is legal in an XML parser. I suspect that this is undefined - however it
must not be 'application-dependent', because otherwise we get different
parser behaviour.  (The use of other connectors (| and ?) is presumably
similar - it's the mechanics of how the entity is retrieved.)
The only argument I can see against this is that it requires all parser
writers who cope with ENTITYs to resolve XLL - and that is quite a strong
argument :-)


Peter Murray-Rust, Director Virtual School of Molecular Sciences, domestic
net connection
VSMS http://www.nottingham.ac.uk/vsms, Virtual Hyperglossary

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