Specify the entry point

To specify an entry point whose name is different from the name of the UDR, put the name of the actual entry point in parentheses after the name of the shared-object file. You must specify an entry point when your UDR has a different name from the UDR that it implements.

The following CREATE FUNCTION statement specifies that the entry point for the object code of the abs_eq() UDR is a C function named abs_equal(): 
CREATE FUNCTION abs_eq(INTEGER, INTEGER)
   RETURNS boolean 
   EXTERNAL NAME '/usr/code/abs.so(abs_equal)'
   LANGUAGE C;

The database server invokes the C function abs_equal() whenever an SQL statement calls the abs_eq() function with two arguments of INTEGER data type.