Today

The question-and-answer session about Peter Grünwald's article at the Commonsense workshop continues, and has gradually extended into a discussion about causality and ramification in general. With one more contribution today - by Eugenia Ternovskaia - it seems it's time to start up the topic-oriented (``panel'') discussion about Ramification and Causality that has been advertised since a while. Authors of additional contributions are asked to specify whether they wish their note to go into the new, topic-oriented debate or to the specific discussion with Peter.

Today's issue contains two contributions: Eugenia's contribution to the new ``ramification and causality'' debate, and also an answer by Eyal Amir to Erik Sandewall's question re his Commonsense workshop paper.

Discussions

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''.

References:

Additional contributions have been received for the discussions about the following article(s). Please click the title of the article in order to see each contribution in its context.

Eyal Amir
Point-Sensitive Circumscription