Antonio,
I was expecting to create a relation such as: using acs_rels to create role and type, as in this sample with videos and thumbs :
select acs_rel_type__create_role(
'video_object', --role
'Video', --pretty_name
'Videos' --pretty_plural
);
select acs_rel_type__create_type(
'video_image_thumbnail_rel', --rel_type
'#acs-subsite.Video_Image_Thumbnail#', --pretty_name
'#acs-subsite.Video_Image_Thumbnails#', --pretty_plural
'relationship', --supertype
'video_image_thumbnail', --table_name
'image_id', --id_column
'video_image_thumbnail_rel', --package_name
'content_item', --object_type_one
'video_object', --role_one
1, --min_n_rels_one
1, --max_n_rels_one
'content_item', --object_type_two
null, --role_two
0, --min_n_rels_two
1 --max_n_rels_two
);