A Simple Declarative Language for Describing Narratives with Actions
Imperial College Research Report DoC 95/12, 1995, last revised July 1996
July 1996 revision appears in the Journal of Logic Programming, Volume
31, 1997
Abstract
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 different
ontology. The semantics of E is based on a simple
characterisation 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.
According to the
second notion, observations made at later times can sometimes 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.
This paper also appears in the Journal of Logic Programming: Special Issue
on Reasoning about Action and Change, Volume 31, Numbers 1-3, edited by
Vladimir Lifschitz, published by Elsevier Science Inc., April-June
1997, pages 157-200.
This paper is available over the Web in postscript form:
LanguageE.ps and in dvi form:
LanguageE.dvi
This research was partly sponsored by the
EPSRC,
under a research project entitled
Logic for Commonsense Reasoning about Continuous Change.