tbloader vs SPARQL INSERT - Why different behaviour with named graphs? - sparql

Question

There is a strange behaviour in the connection of the commandline tools of ARQ, TDB and Named Graphs. If importing data via tdbloader in a named graph it can not be queried via GRAPH clause in a SPARQL SELECT query. However, this query is possible when inserting the data in the same graph with SPARQL INSERT.
I have following assembler description file tdb.ttl:
#prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
#prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
#prefix ja: <http://jena.hpl.hp.com/2005/11/Assembler#> .
#prefix tdb: <http://jena.hpl.hp.com/2008/tdb#> .
[] ja:loadClass "com.hp.hpl.jena.tdb.TDB" .
tdb:DatasetTDB rdfs:subClassOf ja:RDFDataset .
tdb:GraphTDB rdfs:subClassOf ja:Model .
[] rdf:type tdb:DatasetTDB ;
tdb:location "DB" ;
.
There is a dataset in the file data.ttl:
<a> <b> <c>.
Now, I am inserting this data with tdbloader and secondly another triple with SPARQL INSERT, both in the named graph data:
tdbloader --desc tdb.ttl --graph data data.ttl
update --desc tdb.ttl "INSERT DATA {GRAPH <data> {<d> <e> <f>.}}"
Now, the data can be queried with SPARQL via:
$arq --desc tdb.ttl "SELECT * WHERE{ GRAPH ?g {?s ?p ?o.}}"
----------------------------
| s | p | o | g |
============================
| <a> | <b> | <c> | <data> |
| <d> | <e> | <f> | <data> |
----------------------------
Everything seems perfect. But now I want to query only this specifc named graph data:
$ arq --desc tdb.ttl "SELECT * WHERE{ GRAPH <data> {?s ?p ?o.}}"
-------------------
| s | p | o |
===================
| <d> | <e> | <f> |
-------------------
Why is the data imported from tdbloader missing? What is wrong with this query? How can I get results back from both imports?

Answer 1

Try this query:
PREFIX : <data>
SELECT * { { ?s ?p ?o } UNION { GRAPH ?g { ?s ?p ?o } } }
and the output is
----------------------------
| s | p | o | g |
============================
| <a> | <b> | <c> | <data> |
| <d> | <e> | <f> | : |
----------------------------
or try:
tdbquery --loc DB --file Q.rq -results srj
to get the results in a different form.
The text output is makign things look nice but two different things end up as <data>.
What you are seeing is that
tdbloader --desc tdb.ttl --graph data data.ttl
used data exactly as is to name the graph. But
INSERT DATA {GRAPH <data> {<d> <e> <f>.}}
does a full SPARQL parse, and resolves against the base URI, probably looking like file://*currentdirectory*.
When printing in text, URIs get abbreviated, including using the base. So both the original data (from tdbloader) and file:///path/data appear as <data>.
PREFIX : <data>
gives the text output a different way to write it as :.
Finally try:
BASE <http://example/>
SELECT * { { ?s ?p ?o } UNION { GRAPH ?g { ?s ?p ?o } } }
which sets the base URI to something no where near your data URIs so switching off nice formatting by base URI:
----------------------------------------------------------------------------------------------------------------
| s | p | o | g |
================================================================================================================
| <file:///home/afs/tmp/a> | <file:///home/afs/tmp/b> | <file:///home/afs/tmp/c> | <data> |
| <file:///home/afs/tmp/d> | <file:///home/afs/tmp/e> | <file:///home/afs/tmp/f> | <file:///home/afs/tmp/data> |
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