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: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>] ¶
@prefix foaf: <http://xmlns.com/foaf/0.1/>] . ¶
¶
:hevok rdf:type foaf:Person . ¶
:hevok foaf:name "Hevok" . ¶
:eva rdf:type foaf:Person . ¶
¶
Query: ¶
¶
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-nx#>] ¶
PREFIX foaf: <http://xmlns/foaf/0.1/>] ¶
SELECT ?peroson ¶
WHERE ¶
{ ¶
?person rdf:type foaf:Person . ¶
FILTER NOT EXISTS { ?person foaf:name ?name } ¶
} ¶
¶
Result ¶
¶
?person ¶
eva ¶
¶
¶
¶