DMZ 1.7.1 (DataMapper OverZealous Edition)

[eluser]Cord[/eluser]
I have another question relating to what I think would be a deep relationship in DMZ. In my previous question I mentioned a database, db_system. I would like to change the structure of the database slightly such that each databases_users row can below to a group. This would mean that, for example, user X can have access to database Y and Z but with different permission levels. The database structure would look like this:

db_system:
databases
database_id int unsigned auto_increment
host varchar(60)
schema varchar(40)
username varchar(40)
password varchar(30)
dbdriver varchar(10)
dbprefix varchar(20)
pconnect bit(1)
db_debug bit(1)
cache_on bit(1)
cachedir varchar(255)
char_set varchar(10)
dbcollat varchar(20)

users
user_id bigint unsigned auto_increment
username varchar(64)
password varchar(40)

groups
group_id smallint unsigned auto_increment
description varchar(64)
access_level int

databases_users
database_id int unsigned
user_id bigint unsigned
group_id smallint unsigned

How would I represent this relationship in the DMZ models? Clearly I would need a Databases and a Users model, and each would have a $has_many relationship with the other. But how do I add the relationship with groups, and then reference and use the `databases_users.group_id` relationship in a meaningful way?

Thanks again,
Cord