[JENA-2176] TDB2 queries can execute quadpatterns with a literal in the subject position

• Type: Question
• Status: Closed
• Priority: Major
• Resolution: Information Provided
• Affects Version/s: Jena 4.2.0
• Component/s: TDB2
• Assignee: Unassigned
• Reporter: Justin
• Created: 05/Oct/21 00:49
• Updated: 07/Oct/21 12:57
• Resolved: 07/Oct/21 12:16

Description

Hello,

If you try to put a triple into a TDB2 with a literal in the subject position you get the following:

 ERROR riot :: [line: 6, col: 18] Subject is not a URI or blank node

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:

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"| | |

--------------------------------------------

Doesn't this:

 00:32:00 INFO exec :: TDB
 (quadpattern (quad <urn:x-arq:DefaultGraphNode> "lala" ?p ?o1))
 00:32:00 INFO exec :: Execute :: "lala" ?p ?o1

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?