 Intuitively, it suffices to introduce new entities into the domain of discourse. This approach lies at the heart of dynamic semantic theories such as Discourse Representation Theory (Kamp and Reyle 1993, and see also the entry on  Discourse Representation Theory)  or File Change Semantics (Heim 1982). We will need an update procedure that introduces new actions/events into the discourse model but is compatible with the non-monotonic semantics introduced so far. Following van Lambalgen and Hamm (2005) we will use integrity constraints—a device from database theory (for a more complete and formal treatment the reader is referred to Kowalski 1995 and van Lambalgen and Hamm 2005: ch. 8)—to implement the notion of a minimal update of a discourse model. Consider discourse (50). 