def get_relationships_on_date(self, from_=None, to=None):
raise Unimplemented()<EOL>
Gets a ``RelationshipList`` effective during the entire given date range inclusive
            but not confined to the date range.

        arg:    from (osid.calendaring.DateTime): starting date
        arg:    to (osid.calendaring.DateTime): ending date
        return: (osid.relationship.RelationshipList) - the relationships
        raise:  InvalidArgument - ``from is greater than to``
        raise:  NullArgument - ``from`` or ``to`` is ``null``
        raise:  OperationFailed - unable to complete request
        raise:  PermissionDenied - authorization failure
        *compliance: mandatory -- This method must be implemented.*