Alternative files for a resource, definited separately to the main resource.
ref,int(11),
resource,int(11),
name,varchar(100),
description,varchar(200),
file_name,varchar(200),
file_extension,varchar(10),
file_size,bigint(20),
creation_date,datetime,
unoconv,int(11),
alt_type,varchar(100),
page_count,int(11),
