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RE: baseURI - SPARQL endpoint - Named Graph

From: Hans Teijgeler <hans.teijgeler@quicknet.nl>
Date: Thu, 6 Jul 2006 09:44:53 +0200
To: "'Richard Newman'" <r.newman@reading.ac.uk>
Cc: "'SW-forum'" <semantic-web@w3.org>, "'Paap, Onno'" <onno.paap@gmail.com>, "'Benjamins, Robin'" <rxbenjam@bechtel.com>
Message-ID: <000601c6a0d0$157ccce0$6c7ba8c0@hans>
Richard,
 
Thanks again!
 
To make sure that I understood you correctly (and asking some further
questions):

*	

	the base URI is there for convenience only. That convenience is
that, when a base URI is defined, rdf:resource="#identifier" means
"baseURI#identifier" (why not a namespace used then?). I guess that the
choice of a base URI is based on maximum convenience (i.e. usable for the
maximum number of resources) rather than on some physical location (e.g. a
triple store)
*	

	a SPARQL endpoint can be any URI, provided that a SPARQL service is
behind it; HYPERLINK
"http://www.pqr-ltd.com/p4502"http://www.pqr-ltd.com/p4502 could be such an
endpoint URI, provided that p4502 would lead to a SPARQL service (I still
need some clarification about what the latter really means in layman terms;
is an endpoint, like that p4502, a.k.a. fragment? (though not the same, of
course))
*	

	Named Graphs have nothing to do with endpoints, they are accessible
"behind" an endpoint (correct?)

Regards,
Hans

   _____  

From: semantic-web-request@w3.org [mailto:semantic-web-request@w3.org] On
Behalf Of Richard Newman
Sent: Wednesday, July 05, 2006 19:58
To: Hans Teijgeler
Cc: 'SW-forum'; 'Paap, Onno'; Benjamins, Robin
Subject: Re: baseURI - SPARQL endpoint - Named Graph



The data in a quad store has been mapped from some application to the ISO
15926 format, and is owned by the owner of the quad store. All other data
must be fetched from the other stores.
 
Each quad store has its own SPARQL endpoint, and its own base URI (but we
don't know whether that base URI is necessary for that endpoint or not)


The base URI in SPARQL is a syntactic convenience;

BASE <HYPERLINK "http://example.com/"http://example.com/>

... <horse> ...

is the same as saying

... <HYPERLINK "http://example.com/horse"http://example.com/horse> ...

.

I advise you to forget about base URIs.


RAP supports Named Graphs, and now the plot thickens.... How does that
relate to the endpoint and the base URI of that same store? For your
information: we intend to (mis?-)use the Named Graphs for a
compartimentation of the quad store, e.g. import archive, export archive,
population archive, handover archive, and of course the actual 'payload'
information content.


They don't relate. Your SPARQL queries can reference any named graph you
like, and the default graph is unnamed. The endpoint, similarly, can be any
URI you like*, and the base URI can simply be a useful part of a URI to
shorten your queries.

(If you wish, you can somehow alias a name, which could be the same as the
endpoint, to the default graph, but I don't see the point.)


One last question: is there a mandatory format for SPARQL endpoints? Can
these two endpoints co-exist:  
HYPERLINK "http://www.pqr-ltd.com/p4502/me03"http://www.pqr-ltd.com/p4502/
and  
HYPERLINK
"http://www.pqr-ltd.com/p4502/me03"http://www.pqr-ltd.com/p4502/me03  ?
Is that last slash '/' required?


As far as I know there is no mandatory format. If the two resources
reachable by the above URIs when dereferenced can behave differently (which
they can), then I see no problem with it. I wouldn't imagine a trailing
slash being necessary; both are valid absolute URIs, reachable over HTTP.

HTH, 
-R


* With the obvious restriction that you need to put a SPARQL service behind
it!


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Received on Thursday, 6 July 2006 07:45:21 GMT

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