This is very broad definition, the flexibility hiding in the word 'corresponding', and in the choice of properties to model. In a thermostat, for example, the state of thermometer, together with the fact that its readings correspond to the temperature of the world outside, seems to satisfy this definition (one signal, no internal structure). This fact is explicitly denied in the article, but without clear explanation as to why. A more strict definition will of course be able to win this argument.