Halliday & Matthiessen (2014: 650, 652):
Looked at ‘from below’, these textual resources fall into two categories – those that engender grammatical structure (theme and information) and those that do not (conjunction, reference, ellipsis, lexical cohesion). Looked at ‘from above’, these textual resources are concerned either with textual transitions between messages or with textual statuses of components (elements) of these messages. These two classificatory perspectives are intersected in Table 9-19.
The table indicates that structural and cohesive resources work together in the marking of textual transitions and in the marking of textual statuses. In the latter case, all the resources are indeed textual; but in the former, the structural resources are logical rather than textual – the logical relations of clause complexing. … The table does not include lexical cohesion. This is like reference and ellipsis in that it involves components of messages rather than whole messages; but it often works together with conjunction in the creation of relations in text. We shall thus have occasion to refer to it both in our discussion of textual statuses and in our discussion of textual transitions.