Hi Barry, Ken, This is a follow-up question to this old issue.
After upgrading to OWLIM-SE version 5.5 I am no longer able to restrict the execution to specific named graphs (contexts). I am unable to get the inferred statements, so it seems like the default context is no longer included by supplying <null> to the setReadContext method. I have also tried to replace <null> with http://www.ontotext.com/implicit (as suggested by Barry), but that does not work either. Do you have any suggestions on how to satisfy my requirement with the newer version of OWLIM (and Sesame)? Best regards, Erik From: Barry Bishop [mailto:barry.bis...@ontotext.com] Sent: 7. januar 2013 14:18 To: Wenzel, Ken Cc: Erik Boye; owlim-discussion@ontotext.com Subject: Re: [Owlim-discussion] Inference with named graph (context) Hi Ken, Erik, To reiterate what Ken mentioned, there is no standard place to put inferred statements and OWLIM simply adds these to the default graph. If restricting the execution of certain methods to specific named graphs (contexts) only is required, then it will be necessary to include the default graph. Note that at present OWLIM does not compute inferences at query time, so the default graph can include inferred statements produced from explicit statements not present in the selects contexts. For selecting the named graph, please see the Sesame javadoc: http://www.openrdf.org/doc/sesame2/api/org/openrdf/repository/RepositoryConnection.html This explains how to select the default graph. I believe it is possible to pass something like the following to the vararg parameter for contexts: new URI[] {context1, null, context2} - where 'null' represents the default graph. However, if this fails, then with OWLIM-SE it might be possible to use the special URI for inferred statements: <http://www.ontotext.com/implicit><http://www.ontotext.com/implicit> I hope this helps, barry -- Barry Bishop OWLIM Product Manager Ontotext AD Tel: +43 650 2000 237 email: barry.bis...@ontotext.com<mailto:barry.bis...@ontotext.com> skype: bazbishop www.ontotext.com<http://www.ontotext.com> On 04/01/13 10:47, Wenzel, Ken wrote: Hi Erik, in addition to your specific named graphs, you also need to include the default context (with a null URI) when executing your query. This ensures that the inferred triples can also be read. Unfortunately, at the moment it is not possible to retrieve only those triples which are inferred from a certain combination of named graphs. I also think that it is difficult, if not impossible, to implement this on top of a forward chaining reasoner since it would require to store tons of provenance information. A backward chaining reasoner may be better suited for this usage scenario. Virtuoso provides a mechanism called rule sets. These rule sets are associated with a URI (e.g., <urn:ruleset1>) and are based on RDFS/OWL descriptions retrieved from a combination of named graphs (e.g. <urn:graph1>, <urn:graph2>, ...). When executing a SPARQL query a rule set can be selected with a Virtuoso specific SPARQL extension: define input:inference '<urn:ruleset1>' select ?s where { ?s ?p ?o } Afaik, Virtuoso's rule sets are implemented by using query rewriting. Maybe, OWLIM can implement something comparable for its forward chaining approach? For example, the user may specify multiple rule sets and associated named graphs for the inferred triples: <urn:graph1>, <urn:graph2>, ... => <urn:graph-inferred-with-ruleset1> Now, OWLIM's reasoner is executed for each rule set (and combination of named graphs) instead of using only one global reasoner. I don't know if this approach is scalable since it would produce many duplicated inferred triples and also may lead to many reasoner runs if a named graph is changed that takes part in multiple rule sets. Another approach can be that OWLIM uses some sort of filtering to exclude those inferred triples where not at least one asserted triple within the queried named graphs exists that mentions its subject, predicate or object. I've simulated this approach by using SPARQL filters but it tends to be rather slow with OWLIM SE: select ?o where { ?s ?p ?o filter (!bound(?o) || isLiteral(?o) || exists { graph ?g { { ?o ?p1 ?o1 } union { ?s2 ?o ?o2 } union { ?s3 ?o3 ?o } } } } Note: "!bound(?o)" is not required in this query - I've just included it to demonstrate the generic case. Best regards, Ken From: owlim-discussion-boun...@ontotext.com<mailto:owlim-discussion-boun...@ontotext.com> [mailto:owlim-discussion-boun...@ontotext.com] On Behalf Of Erik Boye Sent: Thursday, January 03, 2013 5:16 PM To: owlim-discussion@ontotext.com<mailto:owlim-discussion@ontotext.com> Subject: [Owlim-discussion] Inference with named graph (context) Hi, We are in the process of establishing an infrastructure for storing and querying power system network models based on OWLIM and Sesame. We need to track different versions of the power system network model (at the same time), and thought could be achieved using named graphs: One named graph per version of the power system network model. The queries that are performed on the power system network model heavily depends on OWLIM inference. With only one named graph in the repository, all works fine. But when there are more than one named graph in the repository, and queries need to be restricted to a specific named graph, our queries fail: To restrict the queries to a specific named graph the following Sesame API method is used: ContextAwareConnection#setReadContexts(URI[]) The problem seems to be related to the fact that statements inferred by OWLIM are stored in the unnamed graph (default context), and therefore not included when restricting the queries to a specific named graph. Is this the expected behavior? If yes, why? And does anyone have a suggestion for a workaround, except from the obvious one: separation on the repository level? Best regards, Erik _______________________________________________ Owlim-discussion mailing list Owlim-discussion@ontotext.com<mailto:Owlim-discussion@ontotext.com> http://ontomail.semdata.org/cgi-bin/mailman/listinfo/owlim-discussion
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