Hello Jörn,

> is there any way to configure the sponger behind this to
> 1. cache its lookups, so don't retrieve graphs already present in the local 
> quad store (the DEFINE get:soft "soft" seems to be what I want, but that only 
> works for graphs mentioned in a FROM or FROM NAMED clause),

It caches things by default and control the expiration of cached copies
by returned HTTP header lines. If a remote tells that the resource
should not be cached or sets very small expiration time then the cache
lifetime can not be lengthen. define get:refresh can force earlier
reloading but can not delay it: it sets maximum allowed refresh time,
not a strict value.

> 2. do n-fetches in parallel and/or,

It tries to fetch in parallel, via async_queue-s of "width" 8.
Unfortunately that happens not in all cases.

> 3. tell me if some object turned out not to be a linked data resource, but 
> just an URL (e.g., in the triple: (dbpedia:Barack_Obama dbpprop:reference 
> <http://www.chicagolife.net/content/politics/Barack_Obama>) )

I'll think what can be done. Right now there's nothing ready-to-use,
because we follow Squids strategy and cache only good results, not
failures. However it's possible to make sample RDF view to render data
from table DB.DBA.SYS_HTTP_SPONGE and get access to status of currently
cached copies.

Best Regards,

Ivan Mikhailov
OpenLink Software
http://virtuoso.openlinksw.com



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