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https://issues.apache.org/jira/browse/JENA-2176?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17425517#comment-17425517
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Andy Seaborne commented on JENA-2176:
-------------------------------------
I hope this has explained the situation.
> TDB2 queries can execute quadpatterns with a literal in the subject position
> ----------------------------------------------------------------------------
>
> Key: JENA-2176
> URL: https://issues.apache.org/jira/browse/JENA-2176
> Project: Apache Jena
> Issue Type: Question
> Components: TDB2
> Affects Versions: Jena 4.2.0
> Reporter: Justin
> Priority: Major
> Attachments: z.rq, z.ttl
>
>
> Hello,
> If you try to put a triple into a TDB2 with a literal in the subject position
> you get the following:
> {noformat}
> ERROR riot :: [line: 6, col: 18] Subject is not a URI or blank node
> {noformat}
> So far so good.
> But since literals can not be in the subject position of a triple then a
> query against a TDB2 should never attempt to find a literal in the subject
> position of a triple, right? It would be a waste of time.
> But if I am reading the logs correctly that is what appears to happen:
> {noformat}
> root@ec6206bb523f:/mnt/tdb_42# cat /mnt/z.ttl
> @prefix ex: <[http://example.com/]> .
> ex:apple ex:hasPart ex:skin .
> ex:skin ex:hasName "Skin" .
> ex:file ex:hasPart "lala" .
> root@ec6206bb523f:/mnt/tdb_42#
> root@ec6206bb523f:/mnt/tdb_42# cat /mnt/z.rq
> prefix ex: <[http://example.com/]>
> select * where
> { ?s ex:hasPart ?o . optional \\{ ?o ?p ?o1 . }
> }
>
> root@ec6206bb523f:/mnt/tdb_42# /mnt/apache-jena-4.2.0/bin/tdb2.tdbloader
> --loc=`pwd` /mnt/z.ttl
> 00:31:49 INFO loader :: Loader = LoaderPhased
> 00:31:49 INFO loader :: Start: /mnt/z.ttl
> 00:31:49 INFO loader :: Finished: /mnt/z.ttl: 3 tuples in 0.07s (Avg: 40)
> 00:31:49 INFO loader :: Finish - index SPO
> 00:31:49 INFO loader :: Start replay index SPO
> 00:31:49 INFO loader :: Index set: SPO => SPO->POS, SPO->OSP
> 00:31:49 INFO loader :: Index set: SPO => SPO->POS, SPO->OSP [3 items, 0.0
> seconds]
> 00:31:49 INFO loader :: Finish - index OSP
> 00:31:49 INFO loader :: Finish - index POS
> root@ec6206bb523f:/mnt/tdb_42# /mnt/apache-jena-4.2.0/bin/tdb2.tdbquery -v
> --loc=`pwd` --query=/mnt/z.rq
> 1 PREFIX ex: <[http://example.com/]>
> 2
> 3 SELECT *
> 4 WHERE
> 5
> { ?s ex:hasPart ?o
> 6 OPTIONAL
> 7 { ?o ?p ?o1 }
>
> 8 }
>
> 00:31:59 INFO exec :: QUERY
> PREFIX ex: <[http://example.com/]>
>
> SELECT *
> WHERE
>
> { ?s ex:hasPart ?o OPTIONAL { ?o ?p ?o1 }
> }
> 00:31:59 INFO exec :: ALGEBRA
> (conditional
> (quadpattern (quad <urn:x-arq:DefaultGraphNode> ?s
> <[http://example.com/hasPart]> ?o))
> (quadpattern (quad <urn:x-arq:DefaultGraphNode> ?o ?p ?o1)))
> 00:32:00 INFO exec :: TDB
> (conditional
> (quadpattern (quad <urn:x-arq:DefaultGraphNode> ?s
> <[http://example.com/hasPart]> ?o))
> (quadpattern (quad <urn:x-arq:DefaultGraphNode> ?o ?p ?o1)))
> 00:32:00 INFO exec :: Execute :: ?s <[http://example.com/hasPart]> ?o
> 00:32:00 INFO exec :: TDB
> (quadpattern (quad <urn:x-arq:DefaultGraphNode> <[http://example.com/skin]>
> ?p ?o1))
> 00:32:00 INFO exec :: Execute :: <[http://example.com/skin]> ?p ?o1
> 00:32:00 INFO exec :: TDB
> (quadpattern (quad <urn:x-arq:DefaultGraphNode> "lala" ?p ?o1))
> 00:32:00 INFO exec :: Execute :: "lala" ?p ?o1
> --------------------------------------------
> |s|o|p|o1|
> ============================================
> |ex:apple|ex:skin|ex:hasName|"Skin"|
> |ex:file|"lala"| | |
> --------------------------------------------
> {noformat}
> Doesn't this:
> {noformat}
> 00:32:00 INFO exec :: TDB
> (quadpattern (quad <urn:x-arq:DefaultGraphNode> "lala" ?p ?o1))
> 00:32:00 INFO exec :: Execute :: "lala" ?p ?o1
> {noformat}
> mean a lookup was done in the TDB2 for a triple with the literal "lala" in
> the subject position? If so, shouldn't lookups like that be ignored as they
> will never find matching triples in the TDB2?
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