Entities and XPointers

David G. Durand dgd at cs.bu.edu
Wed Dec 3 04:01:08 GMT 1997

At 12:26 AM -0000 12/3/97, Peter Murray-Rust wrote:

>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,
><A HREF="foo.xml#DESCENDANT(3,CHAP)">

>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.

Sure, it's a legal URL. However, an XML parser is not required to process
fragment IDs, so it's almost certainly a "broken link" in XML parsers that
don't implement XLL.

I think XLL will have to say whether this is supposed to work in XML
parsers that _do_ implement XLL. I would argue that they should (and that
since XLL should be widely implemented) that it will _eventually_ be
sensible to do. At the moment XLL is still soft enough that a hard and fast
judgement on this issue can't really be given, I think.

. 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.)

no, ? is always legal since it's processed at the server, by definition.
Whether it works (as will all URLs) depends on the server's policy for
reolving the URL's sent to it.

>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 :-)

I think the evident usefulness of this is another strong argument for
implementing XLL widely, and also for making sure that XLL processors are
defined to affect URI (URL) throughout a document, and not just in XLL
specific elements.

  -- David

David Durand              dgd at cs.bu.edu  \  david at dynamicDiagrams.com
Boston University Computer Science        \  Sr. Analyst
http://www.cs.bu.edu/students/grads/dgd/   \  Dynamic Diagrams
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