def model_ids(self, protocol=None, groups=None):
    """Returns a list of model ids for the specific query by the user.
       Models correspond to Clients for the XM2VTS database (At most one model per identity).

    Keyword Parameters:

    protocol
      Ignored.

    groups
      The groups to which the subjects attached to the models belong ('dev', 'eval', 'world')
      Note that 'dev', 'eval' and 'world' are alias for 'client'.
      If no groups are specified, then both clients are impostors are listed.

    Returns: A list containing all the model ids (model <-> client in XM2VTS) belonging
             to the given group.
    """

    return [client.subid for client in self.models(protocol, groups)]