On 06/05/2022 16:34, Nouwt, B. (Barry) wrote:
Just tried to move the VALUES clause of the second query inside the WHERE
clause and now it gives the same result as the first query. I am using the
Query# setValuesDataBlock(...) method to set the values programmatically. Can I
control where this method puts the VALUES clause?
yes - by syntax.
If it is outside the WHERE pattern at the end, the query is
"do WHERE pattern, THEN join with the values"
so filtering happen before ?sat value is handled. It is an unbound
variable in FILTER NOT EXISTS
FILTER NOT EXISTS {
?anyVariableNameNoWheerElseInTheQuery a ?someClass
}
If it is first then the query is
"join(values and ?req a ?someClass) then filter."
?sat set by the VALUES, then FILER NOT EXISTS happens.
so the order affects whether VALUEs is before or after the filtering.
Hence whether ?sat is an unboudn valriable or a single term and in NOT
EXISTS that very different.
Andy
Regards, Barry
-----Original Message-----
From: Nouwt, B. (Barry) <[email protected]>
Sent: vrijdag 6 mei 2022 17:26
To: [email protected]
Subject: RE: SPARQL question
I also tried the two queries below using Virtuoso instead of Apache Jena, but
Virtuoso behaves the same with the first query, but gives the following parse
error with the second query:
Virtuoso S0022 Error SQ200: No column sat.
-----Original Message-----
From: Nouwt, B. (Barry) <[email protected]>
Sent: vrijdag 6 mei 2022 17:21
To: [email protected]
Subject: RE: SPARQL question
Just found the following Stack Overflow question which looks related:
https://stackoverflow.com/questions/56891312/difference-in-performance-between-using-values-keyword-and-using-directly-the-ur
Although they talk mostly about the difference in performance between the two
approaches and not about the difference in semantics.
-----Original Message-----
From: Nouwt, B. (Barry) <[email protected]>
Sent: vrijdag 6 mei 2022 17:16
To: [email protected]
Subject: SPARQL question
Hi everyone, two SPARQL queries which I assumed are the same give different
results in Apache Jena. The two queries are:
SELECT * WHERE {
<https://www.tno.nl/kb1/meta/knowledgeinteractions/react/changed/act/requirement> a
?someClass FILTER NOT EXISTS {
<https://www.tno.nl/kb2/meta/knowledgeinteractions/post/new/act/satisfaction> a
?someClass } }
SELECT * WHERE
{
?req a ?someClass
FILTER NOT EXISTS {
?sat a ?someClass
}
}
VALUES (?req ?sat) {
(<https://www.tno.nl/kb1/meta/knowledgeinteractions/react/changed/act/requirement>
<https://www.tno.nl/kb2/meta/knowledgeinteractions/post/new/act/satisfaction>)
}
Note that the queries are basically the same, but the second query uses the
VALUES keyword to bind the ?req and ?sat variables, while the first query
replaces the actual ?req and ?sat variables occurrences instead.
Does anyone know what I am missing?
Best regards,
Barry
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