Halliday & Matthiessen (1999: 378):
A particular domain model within the ideation base correlates with a particular exchange relationship within the interaction base and together they form the ideational and interpersonal aspects of a register.
An exchange relationship thus has ideational implications: it involves the exchange of some ideational meanings rather than others and it embodies a division of labour between the interactants in the exchange relationship.For example, in a service encounter in a local shop (cf. Halliday & Hasan, 1985; Ventola, 1987), the customer may demand goods and information about goods within the relevant domain and the server supplies these on demand and demands goods (payment) in return; and this involves the general domain of business transaction and the particular domain of the business (e.g. hardware).An exchange relationship thus gives interpersonal values to meanings within the domain model it is associated with.
For example, as we have seen, the ideation base embodies both congruent and metaphorical construals of experience; and these variants will be selected partly according to differences in interpersonal distance along dimensions such as age and expertise.