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- From: Michael Mealling <michael@bailey.dscga.com>
- To: xml-dev@lists.xml.org
- Date: Mon, 27 Nov 2000 10:41:32 -0500
----- Forwarded message from Michael Mealling <michael@bailey.dscga.com> -----
Date: Mon, 27 Nov 2000 07:56:01 -0500
From: Michael Mealling <michael@bailey.dscga.com>
Subject: Re: URNs as SYSTEM IDs
In-reply-to: <"from simonstl"@simonstl.com>
To: "Simon St.Laurent" <simonstl@simonstl.com>
Cc: XML-Dev Mailing list <xml-dev@xml.org>
Reply-to: michaelm@netsol.com
Delivered-to: xml.org-xml-dev@xml.org
User-Agent: Mutt/1.1.2i
On Wed, Nov 22, 2000 at 02:54:31PM -0500, Simon St.Laurent wrote:
> SYSTEM identifiers, or more properly, the SystemLiteral which contains the
> content of the SYSTEM identifier, are defined as URIs, conforming to RFC
> 2396. These URIs are "meant to be dereferenced to obtain input for the XML
> processor to construct the entity's replacement text."
>
> In common practice, that's meant using URLs, typically HTTP-based URLs.
> Validating (and some non-validating) XML parsers tend to report errors when
> they can't retrieve the content referenced by a SystemLiteral, since
> effectively it means that they can't validate the document.
Yep. This has bitten me more than once. My solution has been to
use an entity resolver which, IMHO as a xml non-expert, is the right
way to do it....
> I can't find a validity constraint which mandates this behavior, however.
> It seems like dereferencing is a fundamental quality of SystemLiterals, but
> that dereferencing is somewhat, well, variable. Using URNs - when there
> isn't a whole lot of infrastructure for processing them - strikes me as
> foolhardy, but I can see where they might be attractive from an abstract
> perspective, at least.
Yep. Considering that what XML technology uses as its PUBLIC id would be
considered a SYSTEM id by SGML. There will be several cases where
a URI used as the SYSTEM id is not resolvable via standard, globally
available means.
> I'm worried about this providing yet another interoperability issue inside
> of XML 1.0, but I'm not sure there's a hell of a lot we can do about it,
> except perhaps enjoy a 'lucky dip' (as Rick Jelliffe called it) every time
> we encounter a SystemLiteral.
My hope is that XML parsers will make sure that they have entity
resolvers that allow the local parser to match URIs used in the parsing
process, thus ensuring that parsers don't need access to a network
in order to be able to work. It seems kind of problematic to me to
require that your parser is part of a network in order to use the DTD
that you have locally...
-MM
--
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Michael Mealling | Vote Libertarian! | www.rwhois.net/michael
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----- End forwarded message -----
--
--------------------------------------------------------------------------------
Michael Mealling | Vote Libertarian! | www.rwhois.net/michael
Sr. Research Engineer | www.ga.lp.org/gwinnett | ICQ#: 14198821
Network Solutions | www.lp.org | michaelm@netsol.com
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