Halliday & Matthiessen (1999: 158):
Figure 4-11 summarises the generalised participant roles in diagrammatic form. It shows Process and Medium as a complementarity — the Process is actualised through the Medium; and it represents the other participants as external to this nucleus, indicating the type of role relationship that obtains (x enhancing, + extending and = elaborating).
Blogger Comments:
To be clear, omitted from the diagram is the role relationship of projection, which obtains, for example, between the nucleus and the Range of a figure of sensing or saying (i.e. Phenomenon or Verbiage).