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RE: DAV Schema Assessment (was Re: rfc2518bis DAV DTD ...)

From: Julian Reschke <julian.reschke@gmx.de>
Date: Thu, 16 Oct 2003 09:31:55 +0200
To: <dennis.hamilton@acm.org>, "Stanley Guan" <stanley.guan@oracle.com>, "Julian Reschke" <julian.reschke@gmx.de>, <w3c-dist-auth@w3.org>
Message-ID: <JIEGINCHMLABHJBIGKBCAEDDINAA.julian.reschke@gmx.de>

Dennis,

I think you're still missing a basic fact about WebDAV's extensibility: it
is not centralized, nor linear. There is no common registry. Everybody can
add extension elements anytime. Even if somebody would update that Schema
anytime a new RFC (or Internet Draft) comes out out, there will be a lot of
legal WebDAV messages that won't validate against that schema.

Julian

--
<green/>bytes GmbH -- http://www.greenbytes.de -- tel:+492512807760

> -----Original Message-----
> From: w3c-dist-auth-request@w3.org
> [mailto:w3c-dist-auth-request@w3.org]On Behalf Of Dennis E. Hamilton
> Sent: Thursday, October 16, 2003 1:01 AM
> To: Stanley Guan; Julian Reschke; w3c-dist-auth@w3.org
> Subject: RE: DAV Schema Assessment (was Re: rfc2518bis DAV DTD ...)
>
>
>
> Hi Julian and Stanley,
>
> I have been watching your discussion with interest.  I concur
> that XML Schema should work just nifty for DAV, and the one case
> of concern to me can be handled, with a little care.
>
> Let me summarize:
>
> 1.	XML Schema is able to assess schema validity for documents
> that have arbitrary elements (and attributes) from other
> namespaces.  I see there is an open question on the occurrence of
> arbitrary attributes on DAV elements and that needs to be looked
> at separately (e.g., how to use attributes from the global
> attribute namespace versus ad hoc attributes piled onto the DAV
> element and the element-local namespace -- and whether the second
> should be ever allowed).
>
> 2.	I agree that XML Schema is not an useful way to specify DAV
> elements and their content models in the body of the
> specification. However, having and using XML Schemas for DAV XML
> documents is still an useful option.
>
> 3.	The case of concern for me is that XML Schema assessment
> can be done without doing anything to the document, as Stanley noticed.
>
> 3.1	There is no requirement to provide an xsi:schemaLocation
> list, and there is also no requirement that the XML processor use
> it.  It's all hinting, as I recall.
>
> 3.2	However, XML Schemas are targeted to namespaces (which is
> how the whole document can be assessed for schema conformity even
> when the document is drawn from many namespaces).  Since DAV does
> not use immutable namespaces, but uses an extensible namespace
> with a single namespace URI (DAV:), this means the schema
> definition has to be updated when new official elements are added.
>
> 3.3	The only wrinkle here is that XML processors that do schema
> assessment tend to cache the XML Schema definitions by namespace
> URI.  So when the DAV namespace is given new local names, any
> processor prepared to accept those and provide appropriate schema
> assessment must update its cache with the new schema definition.
> (This is another reason that namespace versioning is useful, but
> ... that's life [;<).  [I think my schema/DTD-validating XML
> editor requires me to flush the whole cache to do that, and
> that's the price I pay for being so picky.]
>
> The datatype model of XML Schema seems to be gaining popularity
> for establishing and expressing the (lexical) datatype of
> simple-element content too.  So there is already a source of
> data-type tags (and new schema-defined ones) that can be supplied
> as attributes of property elements conveyed in DAV <prop> listings [;<).
>
> -- Dennis
>
> -----Original Message-----
> From: w3c-dist-auth-request@w3.org
> [mailto:w3c-dist-auth-request@w3.org]On Behalf Of Stanley Guan
> Sent: Wednesday, October 15, 2003 13:41
> To: Julian Reschke; w3c-dist-auth@w3.org
> Subject: Re: rfc2518bis DAV DTD (was Re: How to use DTDs, or not ...)
>
>
>
> Julian,
>
> See my comments inline!
>
> Thx,
>
> -Stanley
>
> ----- Original Message -----
> From: "Julian Reschke" <julian.reschke@gmx.de>
> To: "Stanley Guan" <stanley.guan@oracle.com>; <w3c-dist-auth@w3.org>
> Sent: Wednesday, October 15, 2003 11:32 AM
> Subject: RE: rfc2518bis DAV DTD (was Re: How to use DTDs, or not ...)
>
>
> [ ... ]
>
> >
> > Last time was dicussed I was told that this will not allow new extension
> > elements from the DAV: namespace.
>
> True.  But, new DAV extension elements should be explicitly listed in
> the "choice" component.  So, any bogus element in DAV: namespace
> can be caught.
>
> [ ... ]
> >
> > > > - arbitrary properties are allowed
> > >
> > > I think, you can collect all server supported DAV: properties in
> > > a single complexType using "choice" component.  Then, using
> > > "extension" component to extend different capabilities into the
> > > final set.
> >
> > Sorry. I wanted to say "attributes".
>
> I thought we want to be loose on what can be allowed at element
> level.  Within each element, don't we want all attributes to be
> explicitly spelt out?  Why do we need arbitrary attributes to be
> allowed on any specific DAV: element?
>
> If elements belong to the following category:
>    <xs:any namespace="##other" processContents="lax"/>,
> then any arbitrary attributes can be allowed in them.
>
> [ ... ]
>
>
>
Received on Thursday, 16 October 2003 03:32:11 GMT

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