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 it's 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.
Examples:
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 it's 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"
