W3C home > Mailing lists > Public > semantic-web@w3.org > May 2009

Re: Dereferencing a URI vs querying a SPARQL endpoint

From: Hugh Glaser <hg@ecs.soton.ac.uk>
Date: Wed, 20 May 2009 21:14:56 +0100
To: Daniel Schwabe <dschwabe@inf.puc-rio.br>, "public-lod@w3.org" <public-lod@w3.org>
CC: "semantic-web@w3.org" <semantic-web@w3.org>
Message-ID: <EMEW3|58bc27f753647fb4e82768a69f29709fl4JLFB02hg|ecs.soton.ac.uk|B379%hg@ecs.soton.ac.uk>
Sorry, I'll try harder :-)
I understand that what you are asking is something like this.
For some sites (including rkbexplorer), when you resolve a URI, it constructs a SPARQL query and returns the result of the query.
This might be all the triples with the subject, or object, or both, or something more complex that takes into account b-nodes.
So it might be nice if somewhere, such as the sitemap.xml, this query was documented.
I think this is exactly what the "slicing" is trying to do, but instead of publishing the actual query, it names the common (obvious) ones to use.
So a "slicing" of "subject" would tell you that you could do the query you say below on the appropriate SPARQL endpoint and get exactly the same thing you would get by resolving the URI.
So I still think that answers your question, but I'm sure you can tell me if it doesn't :-)
And others will say if I am wrong.
Best
Hugh

On 20/05/2009 20:47, "Daniel Schwabe" <dschwabe@inf.puc-rio.br> wrote:

Dan and Hugh,
let me be more specific.
I'm not really advocating that only *one* direction should be returned
(or even both directions).
I am asking a more general question (to which I don't think Hugh really
gave an answer either) which is, is there any query that returns the
same triples as the ones you get when you dereference a URI, in a site
that also provides a SPARQL endpoint?
In the affirmative case, I am suggesting that the corresponding query be
documented in the sitemap.xml document.
Does this make sense?

Cheers
D

On 20/05/2009 14:15, Dan Brickley wrote:
> 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 20:15:55 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 21:45:29 GMT