Univariate Structure

Halliday & Matthiessen (2014: 451):

The tactic structures of complexes are relational in nature; they are the kind of structure that we have called univariate, to distinguish it from the multivariate structures … .  A univariate structure is an iteration of the same functional relationship; … Such iterative structures are unique to the logical mode of meaning; they are formed out of logico-semantic relations.