This table cross-references the tables t_note and t_refdb.
The unique ID of an t_xnote entry is stored as a BIGINT value (INTEGER for SQLite).
This BIGINT value (INTEGER for SQLite) points to the ID of the extended note in the table t_note.
This is the ID of the database item that the note is linked to, stored as a BIGINT value (INTEGER for SQLite).
This field stores which type of database item (reference, keyword, author, periodical) the note is attached to.