We describe a simple declarative language E for describing the effects
of a series of action occurrences within a narrative. E is analogous to
Gelfond and Lifschitz's Language A and its extensions, but is based on a
diifferent ontology. The semantics of E is based on a simple characterisa tion of persistence which facilitates a modular approach to extending the expressivity of the language. Domain descriptions in A can be translated to equivalent theories in E. We show how, in the context of reasoning
about actions, E's narrative-based ontology may be exploited in order to
characterise and synthesise two complementary notions of explanation.
According to the first notion, explanation may be partly modelled as the
process of suitably extending an apparently inconsistent theory written in
E so as to establish consistency, thus providing a natural method, in many
cases, to account for conflicting sets of information about the domain. Ac cording to the second notion, observations made at later times can some times be explained in terms of what is true at earlier times. This enables domains to be given an alternative characterization in which knowledge arising from observations is appropriately separated from other aspects of the domain. We also describe how E domains may be implemented as Event Calculus style logic programs, which facilitate automated reasoning both backwards and forwards in time, and which behave correctly even when the knowledge entailed by the domain description is incomplete.