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RE: use of attribute to qualify property value

From: Yaron Goland <yarong@microsoft.com>
Date: Fri, 21 May 1999 17:11:34 -0700
Message-ID: <3FF8121C9B6DD111812100805F31FC0D08793231@RED-MSG-59>
To: "Chris Kaler (Exchange)" <ckaler@exchange.microsoft.com>, "'jamsden@us.ibm.com'" <jamsden@us.ibm.com>, ietf-dav-versioning@w3.org, w3c-dist-auth@w3.org
Modeling history as a resource actually sounds like a good idea for the very
reason that you want to see history in a bunch of different ways. You can
use the content-negotiation features of HTTP to specify to the history
resource exactly how you would like to view it. Alternatively, you can model
history as a search on a versioned resource. But in either case, modeling
history as a property is a bad idea as properties, by definition, do not
support content negotiation.

As for attributes, the sentence you attribute to me was in fact stated by
Jim Davis. 

My objection to the use of XML attributes is based solely on my assessment
that attributes retard extensibility and therefore, by the very definition
of our mission to create a robust protocol, are a bad design choice. I would
strongly encourage you to read
http://lists.w3.org/Archives/Public/w3c-dist-auth/1998JulSep/0084.html in
order to understand my uniform objection to the use of XML attributes.

			Yaron

> -----Original Message-----
> From: Chris Kaler (Exchange) [mailto:ckaler@Exchange.Microsoft.com]
> Sent: Thu, May 20, 1999 9:58 AM
> To: 'jamsden@us.ibm.com'; ietf-dav-versioning@w3.org;
> w3c-dist-auth@w3.org
> Subject: RE: use of attribute to qualify property value
> 
> 
> The reason we had this was because there are different 
> "types" of histories
> that are available and different ways to "view" the history.  
> We modeled
> this (in this draft) as a property, and rather than having 
> "n*m" properties,
> we used a qualifier.
> 
> I, personally, don't think that modeling history as a 
> resource is viable
> since there are several different ways that I want to view 
> the history.
> History information should be an XML "report".  I also don't 
> share Yaron's
> distaste for attributes.  I guess I'm a little suprised by 
> the statement "It
> seems weird to me that the value one gets back is affected by the
> attribute".  What you get back is a function of the XML tag 
> you request.
> Attributes are qualifiers on the tag, right?  Seems logical 
> to me :-) :-)
> 
> Chris
> 
> -----Original Message-----
> From: jamsden@us.ibm.com [mailto:jamsden@us.ibm.com]
> Sent: Thursday, May 20, 1999 5:03 AM
> To: ietf-dav-versioning@w3.org; w3c-dist-auth@w3.org
> Subject: Re: use of attribute to qualify property value
> 
> 
> 
> 
> The history of a versioned resource doesn't seem like a 
> resource to me, it
> seems
> more like information, meta-data, about another resource of 
> set of related
> resources. This is a generated report, not a resource. Making 
> it a resource
> would likely result in redundant data in many server 
> implementations, and
> interfer with the user's namespace.
> 
> I don't share Yaron's view on the use of XML properties. They 
> have some
> advantages and disadvantages over content model, and DAV should not
> prescribe
> any particular policy. It should be up to the client and data 
> modeler to
> decide.
> See xml-dev for lots of discussion on using attributes vs. content.
> 
> 
> 
> 
> "Geoffrey M. Clemm" <gclemm@tantalum.atria.com> on 05/19/99 
> 05:03:35 AM
> 
> To:   ietf-dav-versioning@w3.org, w3c-dist-auth@w3.org
> cc:    (bcc: Jim Amsden/Raleigh/IBM)
> 
> Subject:  Re: use of attribute to qualify property value
> 
> 
> 
> 
> 
> I believe the problem that led to the use of property attributes was
> the attempt to model the "history" of a versioned resource as a
> property.  If instead we model it as a resource (i.e. a 
> "history resource"
> that contains a collection of revisions), then we can just use
> headers (like the Depth header) to modify the PROPFIND call that
> is applied to this collection.
> 
> Cheers,
> Geoff
> 
>    From: Yaron Goland <yarong@microsoft.com>
>    Cc: w3c-dist-auth@w3.org
>    Date: Mon, 17 May 1999 17:46:57 -0700
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>    As explained in detail in
>    
> http://lists.w3.org/Archives/Public/w3c-dist-auth/1998JulSep/0084.html
> XML
>    attributes are a bad idea.
> 
>    The use of attributes invariably indicates an ill considered data
> structure.
> 
>    In this case they are used to avoid dealing with the 
> issues of properties
> on
>    properties. Let us not avoid these hard problems but 
> grabble them head
> on.
> 
>                   Yaron
> 
>    > -----Original Message-----
>    > From: Jim Davis [mailto:jdavis@coursenet.com]
>    > Sent: Mon, May 17, 1999 4:35 PM
>    > To: ietf-dav-versioning@w3.org
>    > Cc: w3c-dist-auth@w3.org
>    > Subject: use of attribute to qualify property value
>    >
>    >
>    > In at least two places, the DeltaV draft protocol (Kaler et
>    > al, Jan 20,
>    > 1999) uses an attribute value to qualify the value of the
>    > property returned
>    > in a PROPFIND.  (The two places I've noticed are 5.2
>    > defaulthistory, which
>    > uses the limit attribute and 5.4 directlineage, which 
> uses the scope
>    > attribute).
>    >
>    > This is a little funny, for two reasons
>    >
>    > 1. As far as I know, WebDAV has never settled whether XML
>    > attributes are
>    > part of a property value (with the exception of the xml:lang
>    > attribute). A
>    > client can certainly store a property whose value includes
>    > attributes, but
>    > it's not clear that the server MUST preserve the attributes.
>    > (Please don't
>    > argue with me about whether it should or should not, all I am
>    > saying is
>    > that, to the best of my knowledge, it's an unsettled controversy)
>    >
>    > 2. It seems weird to me that the value one gets back is
>    > affected by the
>    > attribute.  It's not like I expect proxies to be caching 
> the values of
>    > PROPFIND, but I would like some guidance as a client writer
>    > about when two
>    > properties can meaningfully be compared.  Clearly, in this
>    > case, they can't
>    > if the attributes differ.  Would you propose that, in
>    > general, a property
>    > can only be compared if all attributes are exactly the same?
>    > This isn't
>    > unreasonable, but I would like this settled for WebDAV in
>    > general, and not
>    > by accidental precedent in DeltaV
>    >
>    > best regards
>    >
>    > Jim
>    >
>    > ps I'm new to DeltaV, apologies if this has already come up
>    >
> 
> 
> 
> 
Received on Friday, 21 May 1999 20:11:50 GMT

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