 For the purpose of this entry, it is interesting to note that the general approach taken is to apply a logic of action, viz. dynamic logic, to model information change. This amounts to an approach in which the epistemic (or doxastic) updates are reified into the logic as actions that change the epistemic/doxastic state of the agent. So, for example in Van Linder et al. 1995 we encounter the actions such as \(\lexpand(\phi)\), \(\lcontract(\phi)\), \(\lrevise(\phi)\), referring to expanding, contracting and revising, respectively, one’s belief with the formula \(\phi\). These can be reasoned about by putting them in dynamic logic boxes and diamonds, so that basically extensions of dynamic logic are employed for reasoning about these updates. It is further shown that these actions satisfy the AGM postulates so that this approach can be viewed as a modal counterpart of the AGM framework. Very similar in spirit is the work of Segerberg (1995) on Dynamic Doxastic Logic (DDL), the modal logic of belief change. In DDL modal operators of the form [\(+\phi\)], [*\(\phi\)] and [\(-\phi\)] are introduced with informal meanings: “after the agent has expanded/revised/contracted his beliefs by \(\phi\)”, respectively. Combined with the ‘standard’ doxastic operator \(B\), where \(B\phi\) is interpreted as “\(\phi\) is in the agent’s belief set”, one can now express properties like [\(+\phi]B\psi\) expressing that after having expanded its beliefs by \(\phi\) the agent believes \(\psi\) (also cf. Hendricks and Symons 2006).