def _string_id(*args):
    """Creates an id for a generic entity, by concatenating the given args
    with dots.

    Parameters
    ----------
    *args: str
        The strings to concatenate

    Returns
    -------
    basestring: an identifier to be used.
    """
    def is_valid(entry):
        return (
            isinstance(entry, str) and
            " " not in entry and
            len(entry) != 0)

    if not all(map(is_valid, args)):
        raise ValueError("One or more of the specified parameters was "
                         "invalid: {}".format(str(args)))

    return ".".join(list(args))