Martin (1992: 51):
The rank scale at the level of discourse proposed originally by Sinclair and Coulthard included three additional ranks, two above the exchange (lesson and transaction) and one below (move). Considerations at the ranks of lesson and transaction will be handled under the heading of genre in this book and will be taken up again in Chapter 7, along with a discussion of why genre is treated as a[n] underlying connotative semiotic rather than a higher rank at the level of discourse semantics…
Treating genre as a connotative semiotic is inconsistent with the meaning of both genre and connotative semiotic. Where 'genre' refers to (a type of) language, a connotative semiotic is not language; it is a semiotic system whose expression plane is language (Hjelmslev 1961), and so: more abstract than language.