Halliday & Matthiessen (1999: 291-2):
It is not difficult to embody these intermediate steps in a form of representation such as the following in Fig. 6-19. This does not incorporate any new features; it merely combines the direction of derivation with the functional labelling. What it does, however, is to model the history of the particular instance, showing what semantic features it has, as it were, picked up along the way. It would be possible to explore many other modes of visual presentation; there is no single ideal form, and the approach will vary according to the purpose of the teacher or researcher. Any picture that brings out the two properties of elasticity and directionality would meet the basic requirements.
