W3C home > Mailing lists > Public > public-lod@w3.org > May 2009

Re: Dereferencing a URI vs querying a SPARQL endpoint

From: Dan Brickley <danbri@danbri.org>
Date: Wed, 20 May 2009 19:15:03 +0200
Message-ID: <4A143A97.7040809@danbri.org>
To: Daniel Schwabe <dschwabe@inf.puc-rio.br>
CC: public-lod@w3.org, semantic-web@w3.org
On 20/5/09 18:59, Daniel Schwabe wrote:
> Dear all,
>
> while designing Explorator [1], where one can explore one or more triple
> repositories that provide SPARQL enpoints (as well as direct URI
> dereferencing), I found the following question, to which I don't really
> know the answer...
>
> For the sake of this discussion, I'm considering only such sites, i.e.,
> those that provide SPRQL enpoints.
> For a given URI r, is there any relation between the triples I get when
> I dereference it directly, as opposed to querying the SPARQL enpoint for
> all triples <r, ?p, ?o> ? Should there be (I could also get <?s, ?p, r>,
> for example) ?
> For sites such as dbpedia I believe that I get the same set of triples.
> But I believe this is not a general behavior.
> Should there be a good practice about this for LoD sites that provide
> SPARQL endpoints?
> At the very least, perhaps this could also be described in the semantic
> sitemap.xml, no?

In general, I'd be wary of doing anything that assumes the direction a 
property is named in is important.

Taking the old MCF example, http://www.w3.org/TR/NOTE-MCF-XML-970624/#sec2.1

the_songlines eg:author bruce_chatwin .

where eg:author has a domain of Document and a range of Person.

Exactly the same information could be conveyed in data where the 
property naming direction was reversed. And case by case, different 
natural languages and application environments will favour slightly one 
direction over the other. Here we could as well have had

bruce_chatwin eg:wrote the_songlines .

or eg:book or eg:pub or eg:xyz, with domain Person, range Document.

As it happens in English, the word "author" doesn't have a natural and 
obvious inverse here but that's incidental. The point is that both forms 
tell you just as much about the person as about the document, regardless 
of property naming and direction. The form using "eg:author" seems to be 
document-centric, but in fact it should equally support UI layers that 
are concerned with the person or the document. It would be dissapointing 
if a UI that was presenting info about Bruce Chatwin was to miss out 
that he was the author of the_songlines, simply because somewhere along 
the line a schema writer chose to deploy a property "author" rather than 
"wrote"...

cheers,

Dan


> [1] http://www.tecweb.inf.puc-rio.br/explorator
Received on Wednesday, 20 May 2009 17:15:52 UTC

This archive was generated by hypermail 2.3.1 : Sunday, 31 March 2013 14:24:21 UTC