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wdrs Error (was Re: isDefinedBy and isDescribedBy, Tale of two missing predicates)

From: Phil Archer <phila@w3.org>
Date: Fri, 05 Nov 2010 13:15:59 +0000
Message-ID: <4CD4038F.3030207@w3.org>
To: "public-lod@w3.org" <public-lod@w3.org>
Forwarding my own message, this time from my w3.org address so it 
reaches the list.

Adding Public POWDER list. Main thread is on
http://lists.w3.org/Archives/Public/public-lod/2010Nov/

It's clear to me that there is an error in wdrs:describedby. And since I 
am one of the originators of it, I'd like to do something about it.

What I wrote, and meant, in the text at [1] was:
"... [wdrs:describedby] is a generic relationship type that does not of
itself imply that the link points to a POWDER document — that is done by 
the specific Media type. The formal definition of describedby is given 
in Appendix D."

Appendix D is where it says:

"The relationship A 'describedby' B asserts that resource B provides a
description of resource A. There are no constraints on the format or
representation of either A or B, neither are there any further
constraints on either resource."

However, later in the same document, at [2] it says

We define the RDF property wdrs:describedby with a domain of
rdf:Resource and a range of wdrs:Document. This is the class of POWDER
documents and is a sub class of owl:Ontology. The meaning of
wdrs:describedby is identical to the describedby relationship type
defined above so that:

http://www.w3.org/2007/05/powder-s#describedby

and

http://www.iana.org/assignments/relation/describedby

So we have a mis-match Either wdrs:describedby has a range of
wdrs:Document (bad) or it has the same semantics as the @rel type
describedby which implies no range at all (good).

I'd like to correct this error!! wdrs:describedby is intended to be used
exactly as is being discussed here - a generic link between A and B such
that B describes A with no constraints at all on either.

Since I can (readily) point to an error in the description of what I
hope is a basically sound design, I'm going to see if I can:

a) add an erratum to the POWDER Rec
b) edit the wdrs namespace documentation

That should I hope, make wdrs:describedby fully usable??

(Looks up W3C process document on getting this done...)

Phil

[1] http://www.w3.org/TR/powder-dr/#assoc-linking
[2] http://www.w3.org/TR/powder-dr/#semlink

On 05/11/2010 12:35, Dave Reynolds wrote:
> On Fri, 2010-11-05 at 07:19 -0400, Kingsley Idehen wrote:
>> On 11/5/10 4:51 AM, Dave Reynolds wrote:
>>> On Thu, 2010-11-04 at 20:58 -0400, Kingsley Idehen wrote:
>>>
>>>> When you create hypermedia based structured data for deployment on an
>>>> HTTP network (intranet, extranet, World Wide Web) do include a
>>>> relation that associates each Subject/Entity (or Data Item) with its
>>>> container/host document. A suitable predicate for this is:
>>>> wdrs:describedBy [2] .
>>> Ian mentioned this predicate in his post.
>>>
>>> Looking at [1] the range of wdrs:describeBy is given as "class of POWDER
>>> documents and is a sub class of owl:Ontology" which seems to make it
>>> unsuitable as a general predicate for the purpose being discussed here.
>>>
>>> Dave
>>>
>>> [1] http://www.w3.org/TR/powder-dr/#semlink
>>>
>>>
>>>
>>>
>> Dave,
>>
>> I am not saying or implying that Ian didn't say this in his post.
>> These issues have been raised many times in the past by others
>> (including myself), repeatedly.
>
> Indeed.
>
> I was only responding on the specific suggestion to use wdrs, not
> intending any broader comment.
>
>> Here's the key difference though, yesterday was the first time that
>> these suggestions were presented as somehow being mutually exclusive
>> relative to use of 303 redirection.
>>
>> I don't want to start another session with Ian, but here is my
>> fundamental issue:
>> Fixing RDF resources doesn't have to be at the expense of 303
>> redirection (mechanism for resolve. At the end of the day there are
>> going to be resolvable object/entity identifiers either side of these
>> predicates, if we are seeking to keep the resulting Linked Data mesh
>> intact etc..
>>
>> "dropping 303" simply didn't need to be the focal point of the
>> conversation. It has nothing to do with why people have been
>> publishing "old school" RDF resources that fail to link the container
>> (rdf doc) with its structured content (triples).
>>
>> I hope I've made my point clear :-)
>
> Yes but I don't think the proposal was to ban use of 303 but to add an
> alternative solution, a "third way" :)
>
> I have some sympathy with this. The situation I've faced several times
> of late is roughly this:
>
> Reasonable and technically skilled person new to linked data reviews the
> field with the intention of trying it out and concludes:
>
> (a) Separating URIs for Things[0] and URIs for Documents containing
> assertions (data, descriptions, attribute values, whatever) about those
> things make sense [1].
>
> (b) I want my Thing URIs to resolve but I don't want to use # URIs for
> reasons foo/bar/baz [2].
>
> (c) The Tag finding [3] means that we cannot use slash URIs for Things
> unless we include a 303 redirect.
>
> (d) Ergo we must use 303.
>
> (e) Whoops this use of 303 is proving to be a barrier to adoption for my
> users, maybe I'll switch to an easier technology [4].
>
> Clearly simply using # URIs solves this but people can be surprisingly
> reluctant to go that route.
>
> I take this discussion to be exploring the question:
>
>          Would a third alternative be possible?  People can continue to
>          use # URIs and to use slash URIs with 303s but would it be that
>          bad if we allowed people to use slash URIs for Things, without
>          the redirect?
>
> The talk of "dropping" and "deprecating" I've heard has been concerned
> with the TAG finding on http-range-14 (which does ban use of slash URIs
> for Things and thus is a genuine, standards-body-backed, objection to
> such a third way) rather than to the use of 303s by those happy to do
> so.
>
> Hope this helps rather than muddies things further.
>
> Cheers,
> Dave
>
> [0] I'm going to trying use the terminology of Thing and Document here
> rather than NIR and IR - inspired by Tim's historical note (thanks to
> Andy Seaborne for point this out):
> http://lists.w3.org/Archives/Public/www-tag/2009Aug/0000.html
>
> [1] Note that some people conclude something more like "this is a
> philosophical distinction that I don't care about, I'll go hang with a
> different crowd". This not the branch we're concerned with here.
>
> [2] See for example the reasons cited in Tim's historical summary note.
>
> [3] http://lists.w3.org/Archives/Public/www-tag/2005Jun/0039
>
> [4] Note that I'm in no way suggesting that 303 redirects is the only or
> the biggest barrier to adoption. It just has a way of triggering
> conversations with users and early adopters that tend to be
> counterproductive.
>
>
>
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Received on Friday, 5 November 2010 13:16:29 UTC

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