Re: Compiling information from several different triplestores

Hi Nicolas,

Short answer: No (at least not yet).

Slightly longer version: There is no standard mechanism to efficiently
combine the data from multiple different stores via a JOIN-like mechanism,
unless you know exactly what you are looking for (FROM+CONSTRUCT might
work then), or your stores are single-vendor partitions that can be used
as both individual stores as well as as a virtual mega store.

Even if the new SPARQL WG adds query federation to the spec, you will 
most probably need a more procedural approach, something like DERI Pipes,
SPARQLMotion, or SPARQLScript*, in combination with store metadata and
stats (à la voiD[1]) and some broker (e.g. Sindice). The pieces are 
currently evolving, but "easy" or "efficient" will need a couple more 
years, I guess. 

I can imagine "query expanders" built on top of voiD and Sindice (or
eqivalents), that take your input query and extend it to a set of 
sub-queries, with each subquery's resource identifiers 
canonicalized/adjusted for the individual target store. Creating such 
a helper service could be possible already today, but probably only 
for very basic sameAs consolidation.

Cheers,
Benji

* disclaimer: I'm involved in the SPARQLScript effort.

[1] http://rdfs.org/ns/void-guide

--
Benjamin Nowack
http://bnode.org/
http://semsol.com/


On 05.05.2009 19:33:13, Nicolas Raoul wrote:
>Hello all,
>
>How can I run a query over several different triplestores ?
>
>For instance, I want to get a list of Anthony's friends.
>Triplestore1 says Jack is Tony's friend.
>Triplestore2 says Tony sameAs Anthony.
>What clever mechanism would undestand that Jack is Anthony's friend?
>Do I have to copy all information from both triplestores my own
>triplestore, or is there something smarter to do ?
>
>Copying all information from external triplestores seems awkward, and
>in some cases might prove impossible (frequent updates, size, load on
>servers).
>Is there an easy solution that I am not aware of?
>Can any triplestore implementation be configured to complement its
>information with information from external triplestores?
>
>Thank you!
>Nicolas Raoul
>http://nrw.free.fr
>
>