The Language E is a simple declarative language
for describing the effects of action occurrences within a given
narrative,
using an ontology of actions, time points and fluents
(i.e. properties which can change their truth
values over time). This paper shows how E may be extended to deal with
ramifications. More precisely, we show how
Language E domain descriptions can
include statements describing permanent relationships or constraints between
fluents, and how the model theoretic semantics
of E can be extended
in an intuitive way to ensure that the effects of actions are
appropriately propagated via such statements, whilst retaining E's
simple approach to the frame problem. We also show how Event
Calculus style logic programs may be used to compute consequences
of such domain descriptions using standard SLDNF, even when only incomplete
information is given about some initial state of affairs. Because of
E's generality, these techniques are easily adaptable to
other formalisms for reasoning about actions, such as the
Language A and the Situation Calculus.
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This paper is published by Linköping University Electronic Press (Recommended citation: Linköping Electronic Articles in Computer and Information Science, Vol. 2(1997): nr 12. http://www.ep.liu.se/ea/cis/1997/012/. October 16, 1997), and is posted and under public review in the News Journal of Electronic Transactions on Artificial Intelligence. It is available over the Web via Linköping University Electronic Press in postscript form: http://www.ep.liu.se/ea/cis/1997/012/cis97012.ps.
Various Prolog program listings associated with this paper are also
available:
A. Complete, executable Prolog programs (with example queries listed in program
comments):