def alias_objective(self, objective_id=None, alias_id=None):
raise Unimplemented()<EOL>
Adds an Id to an Objective for the purpose of creating
        compatibility.
        The primary Id of the Objective is determined by the provider.
        The new Id performs as an alias to the primary Id. If the alias
        is a pointer to another objective, it is reassigned to the given
        objective Id.
        arg:    aliasId (osid.id.Id): the alias Id
        raise:  AlreadyExists - aliasId is already assigned
        raise:  NotFound - objectiveId not found
        raise:  NullArgument - objectiveId or aliasId is null
        raise:  OperationFailed - unable to complete request
        raise:  PermissionDenied - authorization failure
        compliance: mandatory - This method must be implemented.