Link to external database

I want to add a link to an external database, one I developed so its under my control and I can add an additional column. I'll probably use a GUID for it. I want to add the same information into MyVideos121.db and have it imported from, exported to the nfo file.

I'm wondering which is the best tag to use. I initially thought <tag> but I don't know if that will affect performance. There are <status> and <code> which are not used and a) I don't know where they map to in the database and b) if they're not used are they going to disappear?

Any recommendation?

Think foreign key. I want to use one of the columns in MyVideos121.db to store a unique ID (probably a GUID) that will provide a foreign key to my database.