Are you familar with nodeaccess_userreference? I'm trying to make a similar module.

I'm working on my first drupal module. I'm trying to simulate the same end result (ie, the same db actions) as nodeaccess_userreference, but need to use a different approach. A group admin needs to be able to assign/unassign node access to individual pages and individual users all in one fell swoop.

1) Is it drupal-legal to just write these inserts/updates to the db directly?

2) Are node_access and content_field_user_ref the only tables the module writes to?

3) The vid and nid columns in content_field_user_ref appear to contain the same values for each record. What's supposed to be the difference between these cols?

4) It would seem that a user having (or not having) a record in node_access would be sufficient to determine whether he has access to that node. So what does "nodeaccess_userreference" in the Realm field accomplish? Where does that field get read? I'm new to drupal. I've been struggling with this for a while.

Thanks Much.