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Re: isDefinedBy and isDescribedBy, Tale of two missing predicates

From: Phil Archer <phil.archer@talis.com>
Date: Fri, 05 Nov 2010 09:05:09 +0000
Message-ID: <4CD3C8C5.30309@talis.com>
To: Kingsley Idehen <kidehen@openlinksw.com>
CC: "public-lod@w3.org" <public-lod@w3.org>
OK, I need to add my two penneth here.

I wrote a short blog entry-like piece last night [1]. My basic point 
being that I agree wholly with Ian's analysis but disagree with his 
conclusions and I argue the case for a new HTTP status code.

I've taken a keen interest in this kind of thing for a while as it 
chimes with the discussion that went on around identifying metadata for 
a given resource (which is relevant to the work I did on POWDER). 
Metadata discovery was discussed at length in the W3C TAG and is at the 
heart of the Web Linking RFC 5988 [2]. That began life many years ago 
when Mark Nottingham wanted to bring back the HTTP Link Header (formally).

The formal definition of wdrs:describedby is at [3] and 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."

You can use it as the RDF property but it has /exactly/ the same 
semantics as the link relationship that we put into the ATOM registry 
initially and is now included in RFC 5988. In other words these three 
are equivalent (by design)

Link: </doc>; rel="describedby" type="foo/bar";

<link rel="describedby" href="/doc" type="foo/bar">

<> wdrs:describedby </doc>

This morning I've been mulling over the idea of suggesting a new MIME 
type that says "the thing you've asked for isn't an information 
resource" and that /might/ help us out of a double round trip to find 
RDF about such a thing but even that doesn't really get us past the fact 
that 200 means "here's a representation of what you asked for". If I 
dereference a URI that identifies beer and it says 200 OK - I at least 
expect to be able to drink it, not read about it.


[1] http://philarcher.org/diary/303/
[2] http://tools.ietf.org/html/rfc5988
[3] http://www.w3.org/TR/powder-dr/#appD

On 05/11/2010 00:58, Kingsley Idehen wrote:
> All,
> So when all is said an done, post 303 redirection imbroglio, the moral
> of the story *seems* to read as follows:
> When you make a hypermedia based Ontology for deployment on an HTTP
> network (intranet, extranet, World Wide Web) do include a relation that
> associates it with the Properties and Classes that it describes.
> Commonly used predicate for this is: rdfs:isDefinedBy [1] .
> 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] .
> At the current time, most ontologies deployed on the Web do not include
> rdfs:isDefinedBy triples. The same applies to descriptor documents (RDF
> included) currently deployed on the Web re. wdrs:isDescribeBy.
> As a best practice, common use of these predicates would increase
> navigability, link density, and overall cohesiveness of the burgeoning
> Web of Linked Data. It would truly demonstrate practicing what we
> preach, dog-food style!
> Links:
> 1. http://www.w3.org/2007/05/powder-s#describedBy
> 2. http://www.w3.org/TR/rdf-schema/#ch_isdefinedby.
> --
> Regards,
> Kingsley Idehen
> President & CEO
> OpenLink Software
> Web: http://www.openlinksw.com
> Weblog: http://www.openlinksw.com/blog/~kidehen
> Twitter/Identi.ca: kidehen
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Phil Archer
Talis Platform
Web: http://www.talis.com
Tel: +44 1473 434770
Twitter: philarcher1
LinkedIn: http://uk.linkedin.com/in/philarcher
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Received on Friday, 5 November 2010 13:05:04 UTC

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