@classmethod
def get_schema(cls):
    """Returns a dictionary of table schema.

        The dictionary mapping tablenames to the list of column names
        for that table. Both tablenames and columnnames are strings.
        """
    d = {}
    d[cls.OBJECTS] = 'object_id', 'owner_id', 'type'
    d[cls.PARENT_TYPES] = 'id', 'parent_type'
    d[cls.PROPERTIES] = 'owner_id', 'name', 'value'
    d[cls.RELATIONSHIPS] = 'source_id', 'target_id', 'name'
    d[cls.CONNECTED] = 'source_id', 'target_id'
    d[cls.STATES] = 'id', 'state'
    return d
