SPARQL evaluation is bottom-to-top (functional). Evaluate the arguments
then combine them, just like a programming language:
f(3+4, 5+6) => f(7, 11) => ....
Evaluate the two parts:
1/ The inner select evaluates to one row:
?x = <http://dbpedia.org/resource/Dynamic_programming>
?y ="Dynamische Programmierung"@de
2/ The ?x dcterms:subject dbpc:Optimal_control evaluates to two rows:
?x = http://dbpedia.org/resource/Optimal_control
and
?x = http://dbpedia.org/resource/Dynamic_programming
Combine these with a join:
When you join those there is one answer:
?x = <http://dbpedia.org/resource/Dynamic_programming>
There will be no results with
?x = http://dbpedia.org/resource/Optimal_control
It is common to read from top to bottom but it's not always right (and
in the past, ARQ has got this wrong with sub-selects as well).
Andy
--------------------------------------------------------------------------------------
On 07/03/11 15:20, baran_H wrote:
Hello, i test with Joseki 3.4.3
----------------------------------------------------------------
PREFIX dbpc: <http://dbpedia.org/resource/Category:>
PREFIX dbpo: <http://dbpedia.org/ontology/>
PREFIX dcterms: <http://purl.org/dc/terms/>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
SELECT ?x ?y
FROM <http://dbpedia.org/resource/Dynamic_programming>
FROM <http://dbpedia.org/resource/Optimal_control>
WHERE {?x dcterms:subject dbpc:Optimal_control .
{SELECT ?x ?y WHERE
{?x rdfs:label ?y . FILTER (lang(?y) = 'en' || lang(?y) = 'de')
}ORDER BY (lang(?y)) LIMIT 1
}}
----------------------------------------------------------------
WITHOUT LIMIT 1 i get:
<../Optimal_control> "Optimal control"@en
<../Dynamic_programming> "Dynamische Programmierung"@de
<../Dynamic_programming> "Dynamic programming"@en
WITH LIMIT 1 i get:
<../Dynamic_programming> "Dynamische Programmierung"@de
I think now: This is coreect if LIMIT 1 is at the end of the query, but
LIMIT 1 for nested SELECT should effect, like ORDER BY (lang(?y)) does,
only results with identical ?x, because
?x dcterms:subject dbpc:Optimal_control
is outer nested SELECT, in the results this is: <../Dynamic_programming>
and therefore with LIMIT 1 i expect (??) :
<../Optimal_control> "Optimal control"@en
<../Dynamic_programming> "Dynamische Programmierung"@de
thanks, baran.
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