W3C home > Mailing lists > Public > xml-uri@w3.org > May 2000

Re: Namespace-by-retrieval is consistent and coherent

From: Simon St.Laurent <simonstl@simonstl.com>
Date: Sun, 28 May 2000 10:52:18 -0400
Message-Id: <200005281450.KAA10632@hesketh.net>
To: xml-uri@w3.org
At 06:19 PM 5/27/00 -0700, Tim Bray wrote:
>>     DEFINE NAMESPACE EQUIVALENCE AS A BYTE-FOR-BYTE COMPARISON
>>     OF THE RESOURCE AS RESOLVED *AND* RETRIEVED.
>
>I think this proposal is coherent and consistent.  I also think that
>given enough caching smarts, it is viable and implementable.  I'm not
>sure that it has a very good cost-benefit trade-off, but reasonable people
>may differ on this.

I think it's pretty clear from previous discussion that reasonable people
would differ on this.  I don't think namespace values by deferencing is
coherent for a number of simple reasons:

1) Retrieval costs and failures.  Many XML Namespaces currently in use
point to nowhere - deliberately.  Some URI schemes (notably mailto: and
URNs) may not return a resource directly anyway.  Even if it's possible to
retrieve, this adds substantial overhead to processing, and requires
parsers to handle lots of protocols well.  (HTTP redirects are a simple but
ugly case for many XML parsers.)

2) Caching costs and failures.  Caching is useless for resources that
change every nanosecond, and unreliable even for resources that change less
frequently.  Synchronization becomes an issue again.

3) Byte-for-byte vs. semantic understanding.  If I slip and add an extra
line break to the document at the end of a namespace, I've suddenly changed
comparisons against all the other namespaces that use the same schema with
the same meaning?

I think we've moved way way way beyond the 80% of functionality for 20% of
the work idea that informed XML originally.
 
>I could live with #2.  Given a W3C recommendation on what dereferencing
>the namespace name should yield (I recommend a packaging document
compromising
>a single (potentially large and complex) extende XLink), I could be
>enthusiastic about it.  -Tim

I could be enthusiastic about pointing to packaging if:
1) Retrieval wasn't mandatory (for reasons above)
2) Packaging work (based on XLink, RDF, and/or XPDL) actually happened
3) The amount of infrastructure needed for packaging is kept to a
reasonable minimum (remember 80/20), reducing parser bloat while improving
interoperability.

Consistent and coherent, unfortunately, aren't always practical.

Simon St.Laurent
XML Elements of Style / XML: A Primer, 2nd Ed.
Building XML Applications
Inside XML DTDs: Scientific and Technical
Cookies / Sharing Bandwidth
http://www.simonstl.com
Received on Sunday, 28 May 2000 10:50:18 UTC

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