OpenLink Virtuoso (Open-Source Edition)

Hi Kingsley and thanks for the response!

On Monday 29 December 2008 22:19:01 Kingsley Idehen wrote:
> If possible, you can just rebuild the RDF_QUAD table with a different
> primary key, and once done the overhead associated with not specifying a
> graph IRI in the FROM clause re. Virtuoso goes away courtesy of the
> column order (and associated re-indexing) in the revised primary key.
> The command for altering the primary key is:
> alter table db..RDF_QUAD modify primary key (S,P,O,G) ;

I must admit that I do not apciate the full depth of what you are saying 
here. I have done a little more research though, and before diving further 
into your suggestion, I'd like to raise another point.

DESCRIBE isn't well specified, and I hope to join DAWG NG to share my 
experiences. Let us nevertheless see if we can agree on what is the most 
intuitive result. 

For example, I'd expect the result of this query:

PREFIX ms:  <http://www.computas.com/mediasone#>
DESCRIBE ?uri 
FROM <http://msone.computas.no/graphs/>
WHERE {
  ?g a <http://msone.computas.no/graphs/vocab/mediasone#InstanceGraph> .
  GRAPH ?g	
  {
 	?uri	ms:coverArt	<http://ruby3.computas.no/covers/nfi/48739.jpg> .
  }
}

To return the same as this query:


PREFIX ms:  <http://www.computas.com/mediasone#>
CONSTRUCT { ?uri 	?p		?s ;
	ms:coverArt	<http://ruby3.computas.no/covers/nfi/48739.jpg> .
}	
FROM <http://msone.computas.no/graphs/>
WHERE {
  ?g a <http://msone.computas.no/graphs/vocab/mediasone#InstanceGraph> .
  GRAPH ?g	
 {
 	?uri 	?p		?s ;
		ms:coverArt	<http://ruby3.computas.no/covers/nfi/48739.jpg> .
  }
}
 
The latter query returns what I'd expect from them both, whereas the former 
has no result (I've set the default graph both as above, and with a protocol 
query parameter). Again, this can be tested live at 
http://msone.computas.no:8890/sparql

So, then you might say "just use the construct and be done with it, then", but 
that will create troubles later, when I want to set a LIMIT, since I want to 
limit on the number of unique subject URIs, which is what the DESCRIBE in 
practise, whereas the CONSTRUCT would limit on the number of solutions, and I 
don't know how many of them I'd like. Also, the CONSTRUCT is arguably more 
complex (for the programmer) than the DESCRIBE query.
 
Kind regards 

Kjetil Kjernsmo
-- 
Senior Knowledge Engineer
Mobile: +47 986 48 234
Email: kjetil.kjernsmo@computas.com   
Web: http://www.computas.com/

|  SHARE YOUR KNOWLEDGE  |

Computas AS  PO Box 482, N-1327 Lysaker | Phone:+47 6783 1000 | Fax:+47 6783 
1001