Hi Ivan. Thanks for the explanation.
Br, Timo Westkämper On 03/08/2011 05:25 PM, Ivan Mikhailov wrote:
Hello Timo, On Mon, 2011-03-07 at 14:29 +0200, Timo Westkämper wrote:Hi all. How do I correctly bind the named graph context of the following SPARQL query : CONSTRUCT { ?s ?p ?o} FROM ?context WHERE { ?s ?p ?o } I tried the following options CONSTRUCT { ?s ?p ?o} FROM `iri(??)` WHERE { ?s ?p ?o } CONSTRUCT { ?s ?p ?o} FROM iri(??) WHERE { ?s ?p ?o } Both throw Exceptions. What is the right way to do it? I am aware that it works also as CONSTRUCT { ?s ?p ?o} WHERE { graph ?context { ?s ?p ?o } } but I prefer the syntax form using FROM.CONSTRUCT { ?s ?p ?o} WHERE { graph `iri(??)` { ?s ?p ?o } } is the only choice, due to performance implications. The FROM clause needs a constant in order to check at the compile time whether the IRI refers to a graph or a graph group. In first case it can make security checks at the compile time (i.e., once) and not waste time at the run time. In second case, a compile-time check, a run-time check or 50/50 mix of them can be performed, depending on the security policies. FROM without constant would mean that security rules, if they present in the storage, are used at the run time, for every triple that matches every triple pattern in the default graph. This issue can be reproduced if FROM is not specified at all: if security differs from default then the effect is noticeably bad. Best Regards, Ivan Mikhailov OpenLink Software http://virtuoso.openlinksw.com
