How can I obtain the object datatype?
To display the object datatype of a triple in a SPARQL result set, the internal Virtuoso/PL function DB.DBA.RDF_DATATYPE_OF_OBJ can be used, invoked as sql:RDF_DATATYPE_OF_OBJ.
Assume the following scenario:
# Explicit typecast (insert)
SQL> sparql insert into <test_datatype> { <a> <string> "string 1"^^xsd:string . };
callret-0
VARCHAR
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Insert into <test_datatype>, 1 (or less) triples -- done
1 Rows. -- 94 msec.
#Not explicit typecast (insert)
SQL> sparql insert into <test_datatype> { <a> <string> "string 2". };
callret-0
VARCHAR
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Insert into <test_datatype>, 1 (or less) triples -- done
1 Rows. -- 16 msec.
SQL> SPARQL
SELECT ?o (iri(sql:RDF_DATATYPE_OF_OBJ(?o, 'untyped!')))
FROM <test_datatype> { <a> <string> ?o} ;
o callret-1
VARCHAR VARCHAR
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string 1 http://www.w3.org/2001/XMLSchema#string
string 2 untyped!
2 Rows. -- 16 msec.
SQL>