On 26 Dec 2013, at 20:51, Rose Beck <[email protected]> wrote:
> I created my data file containing the following data(try.nq):
>
> <http://dbpedia.org/data/Plasmodium_hegneri.xml> <
> http://code.google.com/p/ldspider/ns#headerInfo>
> _:header16125770191335188966549 <a> .
Ah, here is the issue.
N-Quads _doesn't_ permit relative URIs / IRIs. [1] TDB is being kind /
unhelpful and loading the data as requested, full of relative IRIs.
This is, strictly, broken RDF. The behaviour when you work on it is as a
consequence undefined.
(If you run the data through validation this issue is apparent:
$ riot --validate try.nq
ERROR [line: 1, col: 133] Relative IRI: a
...)
> Then I fired the following SPARQL command:
> root@server:/home/apache-jena-2.10.0/bin# ./tdbquery --time
...
> I got the following output:
> -----------------
> | a | b | c |
> =================
> | <a> | <b> |
The answer is a) correct but b) very unhelpful. These are relative IRIs but no
base is given.
> After this I tried another SPARQL query(given below) for which I obtained
> an incorrect output:
> SPARQL query:
> root@server:/home/apache-jena-2.10.0/bin# ./tdbquery --time
> --loc=/home/Jena/try "select ?a?b?c where{ graph ?j1{?a <b> <
> http://dbpedia.org/data/Plasmodium_hegneri.xml>} }"
> Output:
> -------------
> | a | b | c |
> =============
> -------------
> Time: 0.095 sec
SPARQL, unlike N-Quads, allows relative IRIs. In the absence of a BASE
directive the IRIs are resolved relative to the query itself. In this case the
current directory is used as the base, so <b> is understood as <CURRENT_DIR/b>.
You can see this if you add --explain:
$ tdbquery --explain --loc=try "select ?a?b?c where{ graph ?j1{?a <b>
<http://dbpedia.org/data/Plasmodium_hegneri.xml>} }"
00:58:24 INFO exec :: QUERY
SELECT ?a ?b ?c
WHERE
{ GRAPH ?j1
{ ?a <b> <http://dbpedia.org/data/Plasmodium_hegneri.xml> }
}
00:58:24 INFO exec :: ALGEBRA
(project (?a ?b ?c)
(quadpattern (quad ?j1 ?a <file:///private/tmp/b>
<http://dbpedia.org/data/Plasmodium_hegneri.xml>)))
00:58:24 INFO exec :: Execute :: (?j1 ?a
<file:///private/tmp/b> <http://dbpedia.org/data/Plasmodium_hegneri.xml>)
-------------
| a | b | c |
=============
-------------
<b> is resolved to <file:///private/tmp/b> (I ran this in the temp dir). Thus
no results.
So the short answer is that the input data is broken.
Damian
[1] <http://www.w3.org/TR/n-quads/#sec-iri>
[2] <http://www.w3.org/TR/2013/REC-sparql11-query-20130321/#relIRIs>
