There are several theories of discourse structure for texts: RST (Mann and Thompson, 1987), LDM (Polanyi et al., 2004), the graphbank model (Wolf and Gibson, 2005), DLTAG (Forbes et al., 2003), PDTB (Prasad et al., 2008), and SDRT (Asher and Lascarides, 2003).
data from our corpus rule out DLTAG, LDM, and RST as candidate theories because they posit tree-based discourse structures.