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RE: property value clarification

From: David G. Durand <dgd@cs.bu.edu>
Date: Thu, 29 Oct 1998 08:34:23 -0400
Message-Id: <v04011700b25e0e722fe7@[24.0.249.126]>
To: w3c-dist-auth@w3.org
At 11:42 PM -0400 10/29/98, Jim Davis wrote:
>At 03:56 PM 10/29/98 PST, Jim Whitehead wrote:
>>...My sense of the working group is there does not currently exist any
>>consensus on this topic.  Nor, given the depth of the issues, is it likely
>>that any consensus could be achieved quickly.  My recommendation is to leave
>>this issue unresolved, and be silent on this topic within the spec.

It's not at all clear to me that one can do that:
Either you are allowed to put arbitrary XML in properties, or you are not.
If you are not, then that should be specified (and we could relax the
restrictions later). If you are, then servers must choose _some_
XML-preserving implementation (perhaps literal storage of the string, or
portions thereof).

One of the "properties of properies" is that people can make them up to
solve their representational problems, and so they need to know what the
syntax is).

>I concur, with one exception, namely the xml:lang attribute.  This
>attribute must be recorded in order to provide international support.
>Otherwise there is no way to do correct equality comparisons on properties.

>I asked specifically about this attribute in email on 7/27, the sole reply
>(8/5, from EJW) indicated that it would be preserved.

>It's very important that this attribute be preserved, otherwise DAV is
>limited to English language values only.  (Or to be more precise, you could
>store non-English values, but you couldn't operate on them reliably.)

Right, this is one of many. Jim's example about namespaces is another case:
and it's also a case where serer rewriting is _only_ appropriate if the
client and server are both assumed to have XML processors.

I don't think that XML data handling is so hard that restricting it is
worthwhile.

One table "other_attributes" with columns "attname", "elementreference" and
"value" will handle any number of arbitrary attributes, even in a
relational system.

>But as for all other attributes, I recall Yaron saying that the WebDAV data
>model is *not* XML, rather XML is merely one (of possibly many) on the wire
>transport encodings for WebDAV values.

Fortunately that's not _in_ the standard, is it? The standard defines a
protocol, not a data model. The protocol either allows XML properties, or
some undefined subset of them. The latter is bad (unless we define the
subset) and the former says nothing about how properties must be stored in
the engine.

>If this is indeed the concensus opinion, then  WebDAV is not obligated to
>support every feature of the XML data model.  It is XML that is at the
>service of WebDAV, not the other way around.

That's fine, but if you're going to use the syntax, you need to say
something if parts of that syntax are potentially ignored by servers!

Frankly, accepting full XML properties seems like a no-brainer to me: the
parsers are small, and the data model is simple. (RDBMs are going to have
much more trouble handling nesting than they ever will with attributes).

   -- David

This supports Jim Whitehead's assertion that there is no consensus, but
denies that this is acceptable. If we want to outlaw all attributes other
than a small fixed set, that is OK, though I'd be surprised if anyone can
present an argument as to how that makes a significant savings.
_________________________________________
David Durand              dgd@cs.bu.edu  \  david@dynamicDiagrams.com
Boston University Computer Science        \  Sr. Analyst
http://www.cs.bu.edu/students/grads/dgd/   \  Dynamic Diagrams
--------------------------------------------\  http://www.dynamicDiagrams.com/
MAPA: mapping for the WWW                    \__________________________
Received on Friday, 30 October 1998 08:36:12 GMT

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