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if-statementsparql

SPARQL if-then-else statement

I am trying to create an RDF graph, in which: if ?n1 exists then a triple of the form: <?x ex:n "1"> will be created. Otherwise, a triple of the form <?x ex:n "0"> will be created. My code is the following:

CONSTRUCT {?x ex:n ?result .}

WHERE { 
  ?x ex:n ?n1 .
  BIND (IF(?n1 ="    *"^^xsd:string, "0", "1") AS ?result)
}

However, only the triples where the value of ?n1 exists are created (<?x ex:n "1">). I miss the triples of the form: <?x ex:n "0">. Why does it happen?

Solution

  • " *"^^xsd:string will not check that your string is empty. Instead it literlly means "four spaces followed by an asterisk".

    For checking that a string matches a pattern, you should use the SPARQL REGEX function. So you may want to use REGEX(?n1, "^ *$"), where ^ and $ match respectively the begin and end of the pattern and * is the zero-or-more quantifier.

    CONSTRUCT { ?x ex:n ?result . }
WHERE { 
  ?x ex:n ?n1 .
  BIND (IF(REGEX(?n1, "^ *$"), "0", "1") AS ?result)
}

    EDIT: If you want also to retrieve values for ?x where you dont have <?x ex:n ?n1> but you do have <?id ex:p ?x>, you can do something like this:

    CONSTRUCT { ?x ex:n ?result . }
WHERE { 
  { ?id ex:p ?x . } UNION { ?x ex:n ?n1 . }
  BIND (IF(!BOUND(?n1) || REGEX(?n1, "^ *$"), "0", "1") AS ?result)
}