Re: [Rdfapi-php-interest] SPARQL FROM clause question

[Richard C. <ri...@cy...>]

Hi Onno,

On 3 Apr 2006, at 13:59, Onno Paap wrote:
> I would like to combine different ontology's resident in triple  
> stores on different servers. Eventually, thousands of them.
> I am not certain but I suppose the SPARQL syntax provides for that.
Well ... SPARQL has syntax for querying multiple *graphs*. A graph  
can be anything with a URI.

The question is, what kind of URIs can you use in the FROM clause?  
That depends totally on the triple store/toolkit you're using.

In most SPARQL stores, you can put URIs of RDF files in the FROM  
clause. This means you can query multiple RDF *files* that reside on  
different servers.

What you want to do is query multiple *endpoints*. I don't know of  
*any* tool that can do this yet, but it would certainly be very  
useful and cool. So if you build it, be sure to tell us about it!

Richard

> If not, I can work around it in plain old PHP programming, issuing  
> separate SPARQL queries for separate servers, but I would like to  
> know if that is the course of action or not.
>
> For example, I have two different SPARQL endpoints (they really  
> exist):
> http://www.15926.org/2006/02/oim and
> http://www.15926.org/2006/02/rdl
> with named graphs in them of the same names.
> They are not, but suppose they are on different servers.
> Now I want to combine them like this:
>
> prefix dm: <http://www.15926.org/2006/02/dm#>
> select ?id ?superclass
> from < http://www.15926.org/2006/02/oim>
> from <http://www.15926.org/2006/02/rdl>
> where {
> ?id rdfs:subClassOf ?x .
> ?x owl:hasValue ?superclass .
> ?superclass rdf:type dm:ClassOfInanimatePhysicalObject .
> }
>
> Note: in RAP the namespaces rdfs, owl, and rdf don't need to be  
> declared with prefix.
>
> The top two triples in the where clause work for the .../rdl graph  
> and the bottom for the .../oim graph.
> This combined query doesn't work in RAP SPARQL (I'm using netapi).
> My question is: should it work? Or would it work with different  
> syntax? Or totally not?
> Onno Paap