Looks like the source function feature does not support function overloading. For example, I want to define source function GREATEST(expr1, expr2) for the oracle data source model with different signature of parameters as shown below.
GREATEST (expr1 timestamp, expr2 timestamp) RETURN timestamp;
GREATEST (expr1 integer, expr2 integer) RETURN integer;
But creating two soure function with same name in the JBoss developer studio throws an error "The name GREATEST is the same (ignoring case) as 1 other object(s) under the same parent".
Itis a known issue/limitation with Teiid Designer that you cannot create two procedures with the same name under a given schema. If there isn't an issue already, log one under Teiid Designer.