Martin (1992: 23):
From the perspective of discourse semantics, however, these relationships [cohesive relations] can be construed as "structural", although clearly involving a structure of a non-grammatical kind. This construal is important in order to understand the sense in which the discourse semantic unit text instantiates discourse semantic systems.
 It will be demonstrated in later posts that cohesive relations are not 'structural' — except as a Humpty-Dumptyism.
 This conflates two distinct dimensions of the architecture of SFL theory: realisation and instantiation.
The relation between system, paradigmatic ordering, and text as semantic unit, syntagmatic ordering, is the realisation relation between the paradigmatic and syntagmatic axes. Realisation (symbolic abstraction) is an intensive identifying (token-value) relation.
It is the relation between system, as potential, and text as instance (of the system), that is instantiation. Instantiation is an intensive attributive relation (token to type).