query-answering

Virtuoso management for LUBM

Use the interactive SQL interface: http://localhost:8890/conductor/isql_main.vspx

Load data

To load a single file, use the following

SPARQL LOAD <path-to-file-wo-file-protocol> into graph <graph-name>

+Note that D:/ontologies must be in the DirsAllowed in virtuoso.ini file.
+Make sure the memory options in virtuoso has been properly set to allow for quick loading of large datasets

To load multiple files in a dir, use this:

ld_dir('D:/ontologies/lubm/data/','*.owl','http://swat.cse.lehigh.edu/onto/univ-bench/data')

+If the graph uri is not present, a single filed named 'global.graph' with the default graph name can be put in the dir.

Now verify the list of files to be uploaded by the command:

select * from DB.DBA.load_list;

Now load the files by running: rdf_loader_run();

Verify the list of files again to check if the state is 2 (success)

Test a query to check the number of triple loaded:

SPARQL 
select count(*) from <http://swat.cse.lehigh.edu/onto/univ-bench/data>
where {?s ?p ?o}

-After uploading some files, if the load_lst table is not cleared, you may run into problems. Clear the rows: DELETE FROM DB.DBA.load_list
-Delete a graph with all its triples by SPARQL CLEAR GRAPH <named graph id>
-Check all the named graphs in the databases:

sparql 
SELECT  DISTINCT ?g 
WHERE  { GRAPH ?g {?s ?p ?o} }

Load schema for inferences

First load a schema file:

SPARQL LOAD <http://swat.cse.lehigh.edu/onto/univ-bench.owl> into <http://swat.cse.lehigh.edu/onto/univ-bench.owl>

Note that the above command, for some reason, only works with http protocol. If the schema is a local file, try the other command from DB. E.g., RDF_LOAD_RDFXML_MT

Make a ruleset from it:

rdfs_rule_set ('lubm:schema', 'http://swat.cse.lehigh.edu/onto/univ-bench.owl') ;

Verify if the schema has been properly set:

SELECT *
FROM sys_rdf_schema

Issue queries with inference support

An example:

sparql
DEFINE input:inference 'lubm:schema'
PREFIX ub:<http://swat.cse.lehigh.edu/onto/univ-bench.owl#> 
select ?x 
from <http://swat.cse.lehigh.edu/onto/univ-bench/data>
where { ?x rdf:type ub:Person . <http://www.University0.edu> ub:hasAlumnus ?x }

Major issues with Virtuoso: the automatic inference support did not get correct answers!

To obtain correct answers for LUBM, manual modifications to the data or queries are necessary. In particular, the Entailment section.

We chose the materialization approach, in which first the data is materialized manually using the file

Then the query text is obtained from the 'Query Text With Materialized Entailed Triples' using the file