In a relational clause, the relation is either [assigned] or [non-assigned].
If [assigned], then the ASSIGNMENT TYPE is either [by projection] or [by expansion].
If the ASSIGNMENT TYPE is [by projection], then it is either [mental assignment] — in which case the Attributor or Assigner is conscious — or [verbal assignment].
If [mental assignment], then it is either [cognitive] or [desiderative].If the ASSIGNMENT TYPE is [by expansion], then it is either [elaborating assignment] or [enhancing assignment].
See Halliday & Matthiessen (2004: 217).