Change - Negation

Created on Feb. 23, 2013, 12:27 p.m. by Hevok & updated on March 28, 2013, 7:15 p.m. by Hevok

Negation allows to refer to conditions where an answer exists or does not exists. ¶

For instance making a small select statement on a database with three individuals in it for which not all the name is given but the type Person is defined. ¶

If one wants to select all person from a database where one specific attribute is not available then one can do this with the filter expression NOT EXISTS, where one can say FILTER NOT EXIST the name, or a Triple that has a foaf name in it. With such a simple filter NOT EXISTS one can filter out results and therefore give specific things that should not be provides in the results. ¶

* Filter of Query solutions is done within a FILTER expression using NOT EXISTS and EXISTS

Data: ¶

@prefix : <http://example/>] . ¶
@prefix rdf: <>] ¶
@prefix foaf: <>] . ¶

:hevok rdf:type foaf:Person . ¶
:hevok foaf:name "Hevok" . ¶
:eva rdf:type foaf:Person . ¶

Query: ¶

PREFIX rdf: <>] ¶
PREFIX foaf: <http://xmlns/foaf/0.1/>] ¶
oson ¶
{ ¶
?person rdf:type foaf:Person . ¶
FILTER NOT EXISTS { ?person foaf:name ?name } ¶
} ¶

Result ¶

?person ¶
eva ¶

Comment: Updated entry

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