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Re: Uniform access to descriptions

From: Harry Halpin <hhalpin@ibiblio.org>
Date: Mon, 24 Mar 2008 18:08:20 -0400
Message-ID: <47E82654.3050704@ibiblio.org>
To: wangxiao@musc.edu
Cc: Jonathan Rees <jar@creativecommons.org>, "www-tag@w3.org WG" <www-tag@w3.org>

Xiaoshu Wang wrote:
> Harry Halpin wrote:
> <snip>
>> Sigh. Look, in some cases content negotiation for RDF is not going to
>> work. Resources can be linked to each other to provide descriptions and
>> authoritative meta data. Linking is very powerful. Most people know what
>> links are. Most people have no idea that content negotiation even
>> exists.
>>   
> Are you talking about HTTP LINK: header or HTML <link>.  The latter is
> fine.  What I mean the former is useless.
>>> What is the purpose of Link then? To make a client to read something
>>> and then figuring out where the metadata is? Then, putting the Link in
>>> the content is sufficient.
>>>     
>> Yep, and I might add Yahoo! and others are already moving to supporting
>> this way of adding metadata [1]. I think it's generally a good idea to
>> standardize things that the majority of the Web is moving to.  And in
>> some cases the Link cannot be put directly in the content, and in some
>> cases it can. Please read the GRDDL use-cases [2].
>>   
> Both [1] and [2] are HTML <link>, which is fine and necessary.  But
> not HTTP LINK.
>>> Either way, it makes the use of Link redundant .  Of course, unless we
>>> want to abandon content-negotiation, which I don't think we should.
>>> Otherwise, Link is unnecessary.
>>>     
>> Content negotiation is always an option, but it's one many people don't
>> have access to, because they are in a managed IT environment. How about
>> giving people *more* options for adding metadata to their page, instead
>> of *less*?
>>   
> Content negotiation is an option or less used feature because previous
> to semantic web, there is no need to.  If this issue of "Uniform
> access to descriptions" is about to standardize HTML or XML, that is
> O.K.  But the same rational cannot be applied to HTTP.  If people
> don't have access to configure content negotiation, s/he won't have
> access to modify his HTTP LINK header either.  Again, I might have
> misunderstood what is arguing about here. But if it is intend to add
> LINK header for an HTTP content, my opinion is - no, don't do it.
Glad you agree on the use of "link" in the document itself.

We are thinking that there are cases where people cannot modify content
and still want to HTTP GET the URI of the document the metadata is
*about* (since the Link is to metadata "about" a particular URI). Again,
the use-case in POWDER in particular details this.  The GRDDL use-case
allows us to connect documents to RDF transforms without using it. If
you disagree with these use-cases, that's fine, but you're use-cases and
what you think are useless are different than some other equally valid
users. Also

I have not seen you give an argument about how the use of a "Link"
breaks *anything* much less HTTP. In fact, Link was part of an earlier
HTTP RFC 2068, and was apparently left out as an editorial oversight.

Here is the use-case as attached below. Note that we do not specify URIs
for the XML documents, therefore rending the argument to "just use
conneg" void

>From GRDDL Use-Case document (I think Ian Davis wrote this part..):

"Oceanic is part of a consortium of airlines that have a group
arrangement for the shared supply and use of aircraft spares. The
availability and nature of parts at any location are described by
AirPartML, an internationally-agreed XML dialect constrained by a series
of detailed XML Schema. Each member of the consortium publishes the
availability of their spares on the web using AirPartML. These
descriptions can subsequently be searched and retrieved by other
consortium members when seeking parts for maintenance. The protocol for
use of the descriptions requires invalid documents to be rejected.
Oceanic wishes to also publish RDF descriptions of their parts and would
prefer to reuse the AirPartML documents which are produced by systems
that have undergone exhaustive testing for correctness. There is no
provision in the existing schemas for extension elements and changing
the schemas to accommodate RDF would require an extended international
standardisation effort, likely to take many years. This means they
cannot alter their XML documents to use GRDDL. Using the ability of HTTP
Header Linking Draft to specify Link and Profiles for GRDDL
transformation in HTTP Headers, Oceanic Consortium can serve RDF via
GRDDL without altering their XML documents. "

[1] http://www.w3.org/TR/grddl-scenarios/#header_use_case
> Regards,
>
> Xiaoshu


-- 
		-harry

Harry Halpin,  University of Edinburgh 
http://www.ibiblio.org/hhalpin 6B522426
Received on Monday, 24 March 2008 22:09:05 GMT

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