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RE: [xml-dev] Re: determining ID-ness in XML
- From: "Bullard, Claude L (Len)" <firstname.lastname@example.org>
- To: David Brownell <email@example.com>, firstname.lastname@example.org
- Date: Thu, 01 Nov 2001 16:36:25 -0600
It isn't wrong, but multiple IDs are really multiple
locator targets. If we want to preseve the notion
of a unique ID for scope, it seems we should separate
this from the notion of multiple IDs which to me,
feels more like a set of secondary keys: that is,
a unique ID is one per, yet other keys can exist
as members of some set for use in a different location
The concept of address target of the locator, is well-understood.
HyTime ISO 10744 at one point proposed an exhaustive set of locator
types based on means of labeling and means of resolution.
The sort of thing you are asking for as I recall was called
a nameloc. For details of this, you could ask Steve Newcomb,
Neill Kipp, etc. Note: It seemed to me at the time that
this was a very good idea that was overcome by the
pursuit of groves. Groves are in themselves, a good
idea, but seem to race past the problem.
A position is not an address. A position is one kind of
property to create an address. Treelocs, for example,
or rellocs. One reason the Hytimers went as far as they did
was in recognition that SGML itself, was simply yet another
notation type and that a reliable addressing system for
integrated open hypermedia systems required a standard
that worked in any notation.
It would illuminating for some to look over Robin Cover's
page for the work on Hytime. I am not advocating it be
adopted but that the thinking in the area of addressing
and location was advanced. It is possible that the web
architecture itself is at a state of evolution where
revisiting such advanced concepts is of benefit. I
will say up front, it is tough reading.
I have to side with Tim here: it will be better to
work the ID problem itself for declararations in
well-formed-only documents. Extending the system
vocabulary by some means (PIs, xml:n, etc) seem
to be the sweet spot of that. Later, perhaps after
looking into the research the SGML community did
on this subject, it would be good to revisit this.
For now, the problem at hand seems to be Xpointers.
From: David Brownell [mailto:email@example.com]
Hence my initial enthusiasm for an xml:id-ish solution, if one could
be found that didn't mandate only one ID per element. (There can be
many reasons to label a node; one-label-per-node restrictions are
trouble when labels get very much use.) Maybe "xml:ids".
> It may take quite a bit of time before finding and making decisions
> for all the corner cases associated to an indirect IDness mechanism.
Where the indirection was the "list the ID attributes in the instance"
(the xml:idatts approach) ... a related issue is that such mechanisms
are error prone. They can work, if everyone agrees.
> If people don't want to do validation, then xml:id should be used, but
> if the document was authored with a DTD in mind, using an indirection
> mechanism to try to bypass the author intent doesn't seems to me to be
> an improvement, quite the opposite.
I think that's mixing several things up. "Wanting to do validation" is a
policy issue, unrelated to author intent, just like "wanting to avoid
reading the external subset". Having a DTD is orthogonal to those,
and is more akin to author intent -- but isn't the same as wanting
to identify particular nodes by name/role (rather than the less stable
notion of "position" or, as Len said, "address").
I think the problem is needing stable node identifiers (by name/role)
that don't force document authors to declare them in internal subsets
(or use Schema-du-jour) to ensure that minimally conformant XML
parsers will see the decls. So the question becomes where they get
identified. A "global" definition, like an "xml:ids" attribute, seems to
be the least invasive/error-prone solution yet proposed.
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