Hi JP,
You can use booleans, strings and numbers for your input parameters:
For example:
INPUT
ADD_HOLE YES_NO
HOLE_DIAMETER NUMBER
NAME_OF_PART STRING
END INPUT
RELATIONS
IF ADD_HOLE == YES
/* DO SOME CALCULATIONS
ENDIF
IF NAME_OF_PART == "TBNC30HS"
/* DO SOME OTHER CALCULATIONS
ENDIF
END RELATIONS