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Re: Can't RDF describe collection resources?

From: Ruben Verborgh <ruben.verborgh@ugent.be>
Date: Thu, 1 Mar 2012 09:17:54 +0100
Cc: public-rdf@w3.org, public-rdf-wg@w3.org, W3C SWIG Mailing-List <semantic-web@w3.org>
Message-Id: <A7B62EF4-2647-49F2-A9B6-8BE3ED9A9B2C@ugent.be>
To: Michael Hausenblas <michael.hausenblas@deri.org>
Hi Michael,

> Are you aware of http://sioc-project.org/ …?

Thanks for your reply. I’m aware of the SIOC project.
As far as I can see, they do not have a solution for this problem. While they have the :has_reply predicate, they do not have a mechanism to identify all replies to a post.

Note that the “blog post” use case is just an example. In fact, it could be anything collection-related (the relation from a book to its reviews, from a social graph to its members, …).

The general question is:
RDF is great to express individual relations between resources A and B1, B2, B3…
but how can it express the relation between A and the set of all resources Bx?

Best,

Ruben

> On 1 Mar 2012, at 07:28, Ruben Verborgh wrote:
> 
>> Dear Semantic Web enthousiasts,
>> 
>> Suppose we have a Web application for blogging:
>> - /posts/35 is a blog post
>> - /posts/35/comments are the comments to that post
>> - /posts/35/comments/3 is a specific comment to this post
>> 
>> In RDF, it is straightforward to make the relation between the blog post and a specific comment:
>> </posts/35> :hasComment </posts/35/comments/3>.
>> It is also easy to describe the relation between a specific comment and all comments:
>> </posts/35/comments/4> :memberOf </posts/35/comments>.
>> 
>> However, how do we indicate the relationship between the blog post and *all* comments that belong to it?
>> I.e., what is the relationship between </posts/35> and </posts/35/comments> ?
>> 
>> One could make a new predicate for that of course:
>> </posts/35/> :hasComments </posts/35/comments>.
>> But then, we still have to explain the relation between :hasComments and :hasComment; and we’d have to do that for every such plural predicate.
>> 
>> This seems to be a fundamental problem.
>> Clearly, the resource “comments on blog post 35” exists, but there doesn’t seem to be a straightforward way to describe it in RDF.
>> RDF lists will not be sufficient: they could indeed explain the relation between a specific comment and all comments, but not the relation between all comments and the blog post.
>> Also note that the indirect relation “_:x :hasComment _:y. _:y :memberOf _:z” is not sufficient: a blog post can have no comments, but even then it still has an (empty) comments resource.
>> 
>> Have you encountered this issue and how do you solve it?
>> 
>> Kind regards,
>> -- 
>> Ruben Verborgh
>> http://twitter.com/RubenVerborgh
>> PhD Student at Multimedia Lab – IBBT / ELIS, Ghent University, Belgium
>> 
>> Make your hypermedia API ready for intelligent agents via http://restdesc.org/.
>> 
>> 
> 
Received on Thursday, 1 March 2012 08:18:39 GMT

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