def metadata_entry_to_tuple(metadata_entry):
    """Converts a lxml.objectify.ObjectifiedElement metadata entry to a tuple.

    The metadata entry object is converted into a simple (key, value) tuple.

    :param lxml.objectify.ObjectifiedElement metadata_entry: an object
        containing MetadataEntry XML data. This tag is a child tag of
        EntityType.Metadata XML.

    :return: a key-value tuple respresnting the metadata entry. Both key and
        value will be strings.

    :rtype: tuple
    """
    key = metadata_entry.Key.text
    value = metadata_entry.TypedValue.Value.text
    return key, value
