ARQ - Filter Forms

This page describes function-like operators that can be used in expressions, such as FILTERs, assignments and SELECT expressions.

These are not strictly functions - the evaluation semantics of custom functions is to evaluate each argument then call the function with the results of the sub-expressions. Examples in standard SPARQL include bound, which does not evaluate a variable as an expression but just tests whether it is set or not, and boolean operators || and && which handle errors and do not just evaluate each branch and combining the results.

These were previously ARQ extensions but are now legal SPARQL 1.1


The IF form evaluates its first argument to get a boolean result, then evaluates and return the value of the second if the boolean result is true, and the third argument if it is false.


IF ( ?x<0 , "negative" , "positive" )

# A possible way to do default values.
LET( ?z := IF(bound(?z) , ?z , "DftValue" ) )


The COALESCEform returns the first argument of its argument list that is bound.

# Suppose ?y is bound to "y" and ?z to "z" but ?x is not.
COALESCE(?x , ?y , ?z) # return "y"

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