What is FEEL?
FEEL (Friendly Enough Expression Language) is a part of the DMN specification of the OMG. It is designed to write expressions for decision tables and literal expressions in a simple way what can easily understand by business professionals and developers.
Unary Tests vs. Expression
FEEL has two entry points: unary-tests and expressions.
Unary-Tests can be used only for input entries of a decision table. They are a special kind of expression with a different grammar. The expression gets the value of the input expression implicitly as the first argument. The result of the expression must be either
// input less than 7
// input is not 2 or 4
// input is between '2015-09-17' and '2015-09-19'
// input is less or equal one day
Expressions can be used everywhere, e.g. in a decision table as input expression or output entry. An expression takes no implicit arguments like unary-tests.
applicant.monthly.income * 12
if applicant.maritalStatus in ("M","S") then "valid" else "not valid"
sum( [applicant.monthly.repayments, applicant.monthly.expenses] )
sum( credit_history[record_date > date("2011-01-01")].weight )
some ch in credit_history satisfies ch.event = "bankruptcy"