Dear Virtuoso Users list,
Virtuoso seems to be my fate, as I've used it several times for
different projects over the past couple of years.
I have a question relating to the SPARQL engine in Virtuoso,
specifically regarding Linked Data URI Dereferencing and Caching. I have
a Virtuoso installation setup on an Amazon EC2 instance, I want to use
it to do Linked Data (cross-site) queries relating to Local Authorities
of the UK (from data.ordnancesurvey.co.uk ).
When I do this query:
SELECT count(?os_lad)
WHERE
{
?os_lad rdf:type
<http://data.ordnancesurvey.co.uk/ontology/admingeo/District> .
?os_lad <http://www.w3.org/2003/01/geo/wgs84_pos#lat> ?lat ;
<http://www.w3.org/2003/01/geo/wgs84_pos#long> ?long
}
I get a count of 199.
Whereas when I do this:
SELECT count(?os_lad)
WHERE
{
?os_lad rdf:type
<http://data.ordnancesurvey.co.uk/ontology/admingeo/District> .
OPTIONAL { ?os_lad
<http://www.w3.org/2003/01/geo/wgs84_pos#lat> ?lat ;
<http://www.w3.org/2003/01/geo/wgs84_pos#long> ?long }
}
I get a count of 400.
Now I know for a fact that there is a lat and a long for every ordnance
survey district graph. It seems to me that my Virtuoso installation has
accessed 199 of the lat longs, but not the rest of them.
I've tried all of the various sparql grab options at /sparql... but all
return the same result.
Any thoughts, comments or suggestions would be appreciated.
Many thanks,
--
Daniel Lewis
---
Vanir Systems | http://vanirsystems.com/
Computer Science, Technical Writing & Development
Tel: +447834355516 | Email: dle...@vanirsystems.com
