Characterizing Causal Action Theories by Translating Them to Logic Programs with Answer Set Semantics

PhD Thesis Proposal Defence


Title: "Characterizing Causal Action Theories by Translating Them to Logic 
Programs with Answer Set Semantics"

by

Mr. Haodi ZHANG


Abstract:

Formal reasoning about action has been a central topic in logic-based AI for a 
long time, and motivated much of the early work on nonmonotonic logics. The 
main difficulties have been the frame and the ramification problems. Current 
consensus in the community is that to solve the ramification problem, a notion 
of causality is needed. As a result, there has been much work on causal action 
theories and a variety of languages and semantics have been proposed. These 
existing approaches basically all agree when the set of causal rules is 
stratified. However, when there are cycles in the rules, it is not always clear 
how these rules are going to be represented according to these different 
approaches, and what the correct results are supposed to be.

In our work, we propose a new approach to charactorize and evaluate action 
languages, and apply this approach on two most representative action languages, 
B and C. First we consider a simple language for writing causal action 
theories, and postulate several properties for the state transition models of 
these theories. Then we propose to consider what we call permissible 
translations from these causal action theories to logic programs. We identify 
two sets of properties, and prove that for each set, there is only one 
permissible translation, under strong equivalence, that can satisfy all 
properties in the set. As it turns out, for one set, the unique permissible 
translation is essentially the same as Balduccini and Gelfond's translation 
from Gelfond and Lifschitz's action language B to logic programs. For the 
other, it is essentially the same as Lifschitz and Turner's translation from 
the action language C to logic programs. This work provides a new perspective 
on understanding, evaluating and comparing action languages by using sets of 
properties instead of examples, in the sense that other action languages can be 
similarly characterized, and new action languages defined using different sets 
of properties.


Date:			Thursday, 26 March 2015

Time:                   9:00am - 11:00am

Venue:                  Room 3494
                        lifts 25/26

Committee Members:	Prof. Fangzhen Li (Supervisor)
  			Prof. Qiang Yang (Chairperson)
  			Dr. Raymond Wong
  			Prof. Nevin Zhang


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