 Barwise refines the notion of a situation to that of “site”—a structured object that contains information. We now have sites \(x,\) \(y,\) \(z,\)… and types \(\phi,\) \(\psi,\)…, where \(x:\phi\) is read as the information site \(x\) is of type \(\phi\). With the qualification that the channels may or may not be among the sites, and that \(x\cmapsto y\) is a three-place (ternary) relation between information sites and channels. Barwise formulates the Soundness Axiom for channel theory as follows: