relProperty Re: [uf-rest] Roy Fielding on WebDAV and PROPs

[Mark Nottingham]

For other reasons, I've been thinking of putting together an I-D to  
revive the Link HTTP header, along with a separate header to capture  
the URI(s) of the profile(s) in effect for the content.

Interested?

On 2006/04/12, at 2:55 PM, Dr. Ernie Prabhakar wrote:

> Hi Larry,
>
> On Apr 12, 2006, at 2:11 PM, Larry Masinter wrote:
>> After Yaron's bed time story and a 9 year slumber...
>>
>> What was I thinking? Clearly, URL munging isn't so bad, if you
>> add:
>>
>>> where ",properties" is a site-configurable string. It needs to be
>>> advertised by some sort of site metadata; e.g., in OPTIONS
>
> Right, the key is that it has to be *advertised*, not implicitly  
> *assumed*.
>
>> Putting on a different hat, I'll point out another option ...
>> put the metadata *in* the data:
>>
>>     http://www.adobe.com/products/xmp
>>
>> For the descriptive metadata for which this is appropriate,
>> you don't need a separate URI, the latency of a separate
>> GET request, etc.
>
> Yeah, I think someone has already come up with a convention for  
> embedding metadata in web documents:
>
> http://www.w3.org/TR/REC-html40/struct/global.html#h-7.4.4
>
> :-)
>
> As it happens, these in fact use the same profile as microformats:
>
> http://www.w3.org/TR/REC-html40/struct/global.html#adef-profile
>
> The issue at stake, though, is how to advertise metadata that is  
> *not* a proper part of the actual document, which is why I think we  
> need <link> or Link:
>
> I've started a Wiki page to capture the discussion so far.  Please  
> feel free to add questions or comments; let me know if you need  
> write access.
>
> http://microformats.org/wiki/rest/property
>
> -- Ernie P.
>
> = The Problem =
>
> HTML has long used the [http://www.w3.org/TR/REC-html40/struct/ 
> global.html#h-7.4.4 meta] tag for metadata to describe the  
> ''contents'' of a document.  While this works well for "intrinsic"  
> metadata related to authoring, there's no equivalent function for  
> "extrinsic" metadata provided by the server or external sources.
>
> To address this need, [WebDAV] defined a new set of "PROP" methods  
> to create, search, and retrieve '''properties'''.  Unfortunately,  
> in addition to defining a whole new protocol this violates the  
> [rest]ful notion of each resource having a URL for manipulating  
> it.  This raises the question, "What is the RESTful way to use HTML  
> and HTTP to provide useful properties."
>
> = Proposal =
> == relProperty ==
>
> Our proposal, currentlly called "relProperty", is motivated by the  
> following principles:
>
> # Every property must have at least one well-defined URL which can  
> be retrieved and updated.
> # There must be an easy way to discover all the properties  
> associated with a given document.
> # It must be simple to implement on existing web servers without  
> requiring non-trivial modifications
> # It should respect and build on existing [http://microformats.org/ 
> about/ microformat principles] and practices
> # It should be consistent with URL [[rest/opacity]] (properly  
> understood)
>
> == &lt;link> ==
>
> Together, this implies that that the optimal way to associate a  
> property with a document is via the HTML [ link] tag (or the  
> equivalent HTTP "Link:").  This provides the requisite mechanism  
> for telling the client how to construct an appropriate URL for  
> getting or setting each property, as in:
>
>  &lt;link rel="property" href=".;prop1">
>
> == ;property ==
>
> It is conventional, but not mandatory, to use a semicolon (";") as  
> the first character of each property.  This follows the convention  
> used in, e.g. [http://www.macromedia.com/cfusion/knowledgebase/ 
> index.cfm?id=1c6b723 ColdFusion], and eases human-readability.
>
> = Examples =
> * TBD
>
> = Open Issues =
>
> * Can properties be chained together? If so, are they retrieved in  
> parallel, or would those be subproperties?
> * Would we need to worry about [http://lists.evolt.org/archive/Week- 
> of-Mon-20020114/065707.html semicolon exploits]?
> * Are there other conventions we should follow/avoid?
> * Should the "Link:" tag itself be declared in HTTP "OPTIONS"?
>
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>


--
Mark Nottingham     http://www.mnot.net/