@abc.abstractmethod<EOL><INDENT>def get_installations_by_ids(self, installation_ids):<DEDENT>
return<EOL>
Gets an ``InstallationList`` corresponding to the given ``IdList``.

        In plenary mode, the returned list contains all of the
        installations specified in the ``Id`` list, in the order of the
        list, including duplicates, or an error results if an ``Id`` in
        the supplied list is not found or inaccessible. Otherwise,
        inaccessible ``Installations`` may be omitted from the list and
        may present the elements in any order including returning a
        unique set.

        :param installation_ids: the list of ``Ids`` to retrieve
        :type installation_ids: ``osid.id.IdList``
        :return: the returned ``Installation`` list
        :rtype: ``osid.installation.InstallationList``
        :raise: ``NotFound`` -- an ``Id`` was not found
        :raise: ``NullArgument`` -- ``installation_ids`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

        *compliance: mandatory -- This method must be implemented.*