Yet further along the continuum, we have explicit semantics expressed in a formal language. However, they are intended for human processing only. We can think of this as formal documentation, or as formal specifications of meaning. Some examples of this are: 1. Modal logic is used to define the semantics of ontological categories such as rigidity and identity [Guarino et al. 1994]. These are for the benefit of humans, to reduce or eliminate ambiguity in what is meant by these ideas. [...] Formal semantics for human processing can go a long way to eliminating ambiguity, but because there is still a human in the loop, there is ample scope for errors.