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RE: Logic for extending text XML elements

From: Eric Sedlar <Eric.Sedlar@oracle.com>
Date: Tue, 5 Jun 2001 10:48:44 -0700
To: "Lisa Dusseault" <lisa@xythos.com>, <w3c-dist-auth@w3.org>
Message-ID: <NDBBLFOFMCKOOMBDHDBKAENHCBAA.Eric.Sedlar@oracle.com>
I'm not exactly sure what you mean by container, but you can't extend
simpleType XML elements to become complexType ones (which can contain
subelements) in XML schema via the Schema inheritance mechanism, so
rather than updating the DTD/Schema, the correct answer to me is to use
inheritance of XML datatypes to get the restriction you want and NOT
change existing datatypes.

> -----Original Message-----
> From: Lisa Dusseault [mailto:lisa@xythos.com]
> Sent: Tuesday, June 05, 2001 10:50 AM
> To: Eric Sedlar; w3c-dist-auth@w3.org
> Subject: RE: Logic for extending text XML elements
> 
> 
> I see what you mean, however as we extend WebDAV we frequently update the
> XML Schema/DTD.  E.g. we are considering taking propfind and adding an
> <include> element to a container that coudln't previously hold 
> that element.
> What's the difference between that and updating the schema for an element
> that contains strings?
> 
> Adding new elements to containers that already hold XML elements 
> seems like
> A Good Way to extend DAV.
> Adding new elements to containers that previously only held text 
> seems like
> A Bad Way to extend DAV.  If there's consensus on this, perhaps we could
> state as much.
> 
> lisa
> 
> > -----Original Message-----
> > From: w3c-dist-auth-request@w3.org
> > [mailto:w3c-dist-auth-request@w3.org]On Behalf Of Eric Sedlar
> > Sent: Tuesday, June 05, 2001 10:00 AM
> > To: w3c-dist-auth@w3.org
> > Subject: RE: Logic for extending text XML elements
> >
> >
> > The XML schema for <d:href> should be defined as a simple type (like
> > "anyURI", which subclasses "string"), which disallows element children.
> > I assume the DTD says the same thing (I'm not as familiar with DTD).
> >
> > > -----Original Message-----
> > > From: w3c-dist-auth-request@w3.org
> > > [mailto:w3c-dist-auth-request@w3.org]On Behalf Of Lisa Dusseault
> > > Sent: Tuesday, June 05, 2001 9:29 AM
> > > To: w3c-dist-auth@w3.org
> > > Subject: Logic for extending text XML elements
> > >
> > >
> > > I've run into a minor issue relating to XML syntax and WebDAV
> > > extensibility.
> > >
> > > I'm parsing:
> > > <D:href>http://myserver.com/</D:href>
> > >
> > > Since an XML element can legally contain both text and elements (e.g.
> > > <P>Hello <em>sailor!</em></P>), it's conceivable that in the 
> future the
> > > <href> element could be extended to have:
> > >
> > > <D:href>http://myserver.com/
> > >   <expires>123486</expires>
> > >   more-stuff
> > > </D:href>
> > >
> > > RFC 2518 says:
> > >    "All DAV compliant resources MUST ignore any unknown XML 
> element and
> > >    all its children encountered while processing a DAV method 
> that uses
> > >    XML as its command language."
> > >
> > > That would indicate that I should ignore the <expires> element.
> >  I can do
> > > that.  But what does "ignore" mean?
> > >  - Do I treat it as a separator so that "http://myserver.com/"
> > is one text
> > > child of DAV:href and "more-stuff" is another text child?  
> How do I know
> > > which one to treat as the URL, particularly if they both look 
> like urls?
> > >  - Do I conceptually remove the ignored element?  That would leave
> > > <DAV:href> with a single text child containing white space,
> > approximately:
> > > "http://myserver.com/  more-stuff".
> > >
> > > Since all this is rather ugly, I'd most like to have a sentence
> > > added to RFC
> > > 2518 (section 14?) that states at a minimum that "text elements
> > should NOT
> > > have their syntax extended by adding XML elements because this
> > is unlikely
> > > to be backward-compatible."  I think we already instinctively
> > follow this
> > > guideline, but it's hard to write solid code based on guesses and
> > > predictions that aren't written down.
> > >
> > > Any other proposals or insights?
> > >
> > > lisa
> > >
> > >
> 
> 
Received on Tuesday, 5 June 2001 13:56:49 GMT

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