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RE: WebDAV property schema lookup

From: Julian Reschke <julian.reschke@gmx.de>
Date: Sun, 7 Apr 2002 11:34:05 +0200
To: "Clemm, Geoff" <gclemm@rational.com>, "DAV" <w3c-dist-auth@w3.org>
Message-ID: <JIEGINCHMLABHJBIGKBCOEJKEFAA.julian.reschke@gmx.de>
Geoff,

in general agree that when defining marshalling formats, extensibility
should be planned in and thus attributes can be problematic.

In this particular case however:

- Marshalling data type information using the xsi:type attribute is defined
in XML Schema (datatypes) and already is done in other protocols (like
SOAP). So here I think we should benefit from existing infrastructure (for
instance existing libraries that support XML Schema datatypes)

- WebDAV's multistatus format isn't very extensible itself (although it uses
elements). To be extensible, the actual propery values would need one
additional wrapper, such as:

<response>
  <href>...</href>
  <propstat>
    <prop>
      <wrapper>
        <one-dead-property>...</one-dead-property>
      </wrapper>
      <wrapper>
        <one-dead-property2>...</one-dead-property2>
      </wrapper>
   </prop>
  </propstat>
  ...

or

<response>
  <href>...</href>
  <propstat>
    <prop>
      <one-dead-property>...</one-dead-property>
   </prop>
    <prop>
      <one-dead-property2>...</one-dead-property2>
   </prop>
  </propstat>
  ...


However we don't have that, which makes extending property values using
elements harder than using attributes.

Julian

> -----Original Message-----
> From: w3c-dist-auth-request@w3.org
> [mailto:w3c-dist-auth-request@w3.org]On Behalf Of Clemm, Geoff
> Sent: Saturday, April 06, 2002 10:54 PM
> To: DAV
> Subject: RE: WebDAV property schema lookup
>
>
> I agree that property "metadata" should only be returned
> if the client specifically asks for it.  Along the same lines,
> I would provide a mechanism for the client to ask for specific
> metadata, since it doesn't make any sense to send back to
> the client metadata information that it doesn't understand.
> Finally, I would marshall all of this as XML elements, not as
> attributes.  XML element values are significantly more extensible
> that attribute values, and given the relative infrequency of
> asking for this metadata, the additional bytes required by
> XML elements shouldn't be an issue.
>
> Cheers,
> Geoff
>
> -----Original Message-----
> From: Julian Reschke [mailto:julian.reschke@gmx.de]
> Sent: Saturday, April 06, 2002 10:51 AM
> To: Eric Sedlar
> Cc: DAV
> Subject: RE: WebDAV property schema lookup
>
>
> > From: w3c-dist-auth-request@w3.org
> > [mailto:w3c-dist-auth-request@w3.org]On Behalf Of Eric Sedlar
> > Sent: Tuesday, April 02, 2002 10:52 AM
> > To: Julian Reschke
> > Cc: DAV
> > Subject: Re: WebDAV property schema lookup
> >
> >
> > I don't think that deciding which dead properties are editable
> > will be done
> > on the client, but rather via some server-specific mechanism.
>
> I agree. The question being, how a server decides this for a given dead
> property (it may not be able to do it).
>
> > For example,
> > we would probably say that all dead properties not in the DAV or Oracle
> > namespaces are editable by default, and possibly allow some
> > configuration in
> > a parameter file to list uneditable ones.
>
> That's certainly something that *can* be done.
>
> So how do we proceed?
>
> - I think that what our current draft says is needed as a basis anyway
> - One possible approach would be to get into the schema / model
> business, 
> la Exchange 2000 and Sharepoint
> - A simpler approach would be to define marshalling for the additional
> information you asked for as extensions to PROPFIND/PROPPATCH
>
> For instance, the first two things you asked for (editability and
> visibility) can trivially be marshalled in new property attributes (this
> could be easily added to our existing datatype marshalling):
>
> Proppatch request:
>
> <?xml version="1.0" encoding="utf-8" ?>
> <D:propertyupdate xmlns:D="DAV:"
>    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
>    xmlns:xs="http://www.w3.org/2001/XMLSchema"
>    xmlns:Z="http://www.w3.com/standards/z39.50"
>    xmlns:x="http://webdav.org/property-attribute">
>   <D:set>
>     <D:prop>
>       <Z:released xsi:type="xs:boolean" x:hidden="true"
> x:editable="false">false</Z:released>
>     </D:prop>
>   </D:set>
> </D:propertyupdate>
>
> ..
>
> Propfind response:
>
> <?xml version="1.0" encoding="utf-8" ?>
> <D:multistatus xmlns:D="DAV:"
>    xmlns:Z="http://www.w3.com/standards/z39.50"
>    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
>    xmlns:xs="http://www.w3.org/2001/XMLSchema"
>    xmlns:x="http://webdav.org/property-attribute">
>   <D:response>
>     <D:href>http://www.foo.com/bar.html</D:href>
>     <D:propstat>
>       <D:prop>
>         <D:getcontenttype>text/html</D:getcontenttype>
>         <Z:released xsi:type="xs:boolean" x:hidden="true"
> x:editable="false">1</Z:released>
>       </D:prop>
>       <D:status>HTTP/1.1 200 OK</D:status>
>     </D:propstat>
>   </D:response>
> </D:multistatus>
>
>
> Note that this is compatible with RFC2518 as
>
> - old clients will never send the new attributes upon PROPPATCH
> - servers can add the two attributes two the existing property values
> transparently (because they sit in a new namespace which should be ignored
> by old clients)
>
>
> Adding textual descriptions is a bit harder, because it's not as easy to
> marshall them in attribute values (we need to make sure that we properly
> treat language negotation/xml:lang). I wouldn't want to send this
> information with every PROPFIND reply, so we probably would require that a
> client specifically asks for them:
>
> Propfind request:
>
> <?xml version="1.0" encoding="utf-8" ?>
> <D:propfind xmlns:D="DAV:"
>   xmlns:Z="http://www.w3.com/standards/z39.50"
>    xmlns:x="http://webdav.org/property-attribute">
>   <D:prop x:include-descriptions="true">
>     <D:getcontenttype/>
>     <Z:released/>
>   </D:prop>
> </D:propfind>
>
>
> Propfind response:
>
> <?xml version="1.0" encoding="utf-8" ?>
> <D:multistatus xmlns:D="DAV:"
>    xmlns:Z="http://www.w3.com/standards/z39.50"
>    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
>    xmlns:xs="http://www.w3.org/2001/XMLSchema"
>    xmlns:x="http://webdav.org/property-attribute">
>   <D:response>
>     <D:href>http://www.foo.com/bar.html</D:href>
>     <D:propstat>
>       <D:prop>
>         <D:getcontenttype>text/html</D:getcontenttype>
>         <Z:released xsi:type="xs:boolean" x:hidden="true"
> x:editable="false"><x:description
> xml:lang="en">released?</x:description>1</Z:released>
>       </D:prop>
>       <D:status>HTTP/1.1 200 OK</D:status>
>     </D:propstat>
>   </D:response>
> </D:multistatus>
>
>
> Feedback appreciated.
>
> Julian
>
Received on Sunday, 7 April 2002 05:34:44 GMT

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