Assign operand

In contrast to ODMG suggestions, OSI only supports '=' as value assign operator and '&=' as reference assign operator. Usually, OSI determines automatically, whether a value or a reference to a value should be assigned. In case of assigning a reference variable to a reference variable it is, however, not clear, whether the reference or the value should be assigned. In this case, the '=' operator will assign the value and the '&=' operator the reference.