Colloquium on Reasoning about Actions and Change

Causality and ramification are two important and closely related topics in knowledge representation and reasoning about actions and change. There was always an obvious need for a separate ENRAC panel on this topic. Concretely, the panel was created in March, 1998, when the discussion about Peter Grünwald's article at the Commonsense workshop generalized to a broader debate about causal approaches to ramification. That debate was transferred to the present, newly created panel. We will also invite the panelists and participants in the causality panel at the NRAC workshop of IJCAI 1997 (chaired by Michael Thielscher) to write up their contributions and include them here.

 

2.3

Eugenia Ternovskaia

Erik Sandewall wrote:

maybe the section on "related work" in research papers ought not to be our only mechanism for assembling topic-specific surveys and bibliographies, and possibly the present debate forum could serve as a complement. Additional contributions are invited to this account of recent history, therefore.

A few notes about earlier work on the solution to the frame and ramification problems based on the notion of causation.

In connection with the frame problem, an important step forward was the idea

1. to characterize the conditions making fluent F true and the conditions making it false separately, and, at the same time,

2. to say that actions produce no other effects using a minimization policy.

I think it was proposed in Lifschitz's 1987 paper [s-Brown-87-35], but it needs a check. Vladimir, could you remind us?

Reiter, basing his solution on the previous work by Pednault, Haas and Schubert, appeals to the same two principles [s-Lifschitz-91-359]. He specifies the conditions making a fluent to hold and not to hold by FO formulas  gamma⁺  and  gamma^- . Instead of explicit minimization, he uses the Causal Completion Assumption.

The main lesson we can derive from this work is that no special non-logical symbol (predicate) is necessary to capture causal information in classical logic.

With respect to the ramification problem, Elkan [c-cscsi-92-221] considers a ``stuffed room'' domain, a variant of the ``suitcase example''. He argues that the ambiguity problem can be resolved using an explicit notion of causation. He uses two predicates,  causes(a, s, f)  to be read ``executing action  a  in state  s  causes fluent  f  to become true'', and  cancels(a, s, f)  saying ``executing action  a  in state  s  causes fluent  f  to become false''. In order to specify that actions produce no other effects, he uses ``bidirectional implication as a minimization operator'', i.e., he completely characterises predicates ``causes'' and ``cancels''.

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