Limiting the number of Triples being cached when importing a Sparql EndPoint

[Maatary Okouya]

Hi, 

I had to substantially increase the Java Heap of Topbraid, to successfully add a sparql end point to a database running on my machine. 

TBC was crashing depending of the amount of data that i loaded on my triple store. It seems that TBC by default, load the all content coming from the TripleStore endpoint. 

Is there a way to limit that, or else to stop TBC from Caching ?

Also maybe the best would be to describe, what is the point of importing a sparql endpoint, as opposed to using SERVICE. What is the original intent of that functionality ? 

Basically could it be that it is to import a model in memory right ? and work with it as if you had an RDF file ?

[Holger Knublauch]

Hi Maarary,

I assume you are referring to the SPARQL Endpoint graphs stored via .sparqlep files and created via "Create Connection File for SPARQL Endpoint"?

That feature is allowing users to treat any (remote) SPARQL endpoint as a normal RDF graph. Basically each find SPO query is turned on the fly into a corresponding SPARQL SELECT ?s ?p ?o query. It is not optimized at all and not recommended for serious work due to its architecture. Among others it also cannot handle blank nodes correctly because the SPARQL protocol doesn't support blank node identity.

If you ask something like ?s ?p ?o (with all three nodes as wildcards) it will indeed end up loading the whole SPARQL end point into a temporary data structure. For medium-sized to large databases this is almost certainly not what you want.

To offer advice on alternatives, you may want to tell us more about what you are trying to do. If you just want to query a remote end point for certain data triples, you could switch to using SERVICE. You could embed SERVICE into SPIN rules or magic properties. If you use SERVICE from SPIN rules, you could perform the "inferences" to download the required triples as a batch job.

Regards,
Holger

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