5 research outputs found
Admissible and Restrained Revision
As partial justification of their framework for iterated belief revision
Darwiche and Pearl convincingly argued against Boutiliers natural revision and
provided a prototypical revision operator that fits into their scheme. We show
that the Darwiche-Pearl arguments lead naturally to the acceptance of a smaller
class of operators which we refer to as admissible. Admissible revision ensures
that the penultimate input is not ignored completely, thereby eliminating
natural revision, but includes the Darwiche-Pearl operator, Nayaks
lexicographic revision operator, and a newly introduced operator called
restrained revision. We demonstrate that restrained revision is the most
conservative of admissible revision operators, effecting as few changes as
possible, while lexicographic revision is the least conservative, and point out
that restrained revision can also be viewed as a composite operator, consisting
of natural revision preceded by an application of a "backwards revision"
operator previously studied by Papini. Finally, we propose the establishment of
a principled approach for choosing an appropriate revision operator in
different contexts and discuss future work
AGM 25 years: twenty-five years of research in belief change
The 1985 paper by Carlos Alchourrón (1931–1996), Peter Gärdenfors,
and David Makinson (AGM), “On the Logic of Theory Change: Partial Meet
Contraction and Revision Functions” was the starting-point of a large and
rapidly growing literature that employs formal models in the investigation
of changes in belief states and databases. In this review, the first twenty five years of this development are summarized. The topics covered include
equivalent characterizations of AGM operations, extended representations of
the belief states, change operators not included in the original framework,
iterated change, applications of the model, its connections with other formal
frameworks, computatibility of AGM operations, and criticism of the model.info:eu-repo/semantics/publishedVersio
Levi and Harper identities for non-prioritized belief base change
In this paper, we investigate the relation between shielded base contraction postulates
and credibility-limited (CL) base revision postulates. More precisely, we identify (i) the
relation between the postulates satisfied by a shielded base contraction operator and the
postulates satisfied by the CL base revision operator that is defined from it by means of the
consistency-preserving Levi identity and (ii) the relation between the postulates satisfied
by a CL base revision operator and the postulates satisfied by the shielded base contraction
operator that is defined from it by means of the Harper identity. Furthermore, we show
that the consistency-preserving Levi identity and the Harper identity establish a one-to one correspondence between the twenty classes of shielded base contractions presented in
[21] and the twenty classes of credibility-limited base revisions presented in [22].info:eu-repo/semantics/publishedVersio
Control room agents : an information-theoretic approach
In this thesis, a particular class of agent is singled out for examination. In order to provide
a guiding metaphor, we speak of control room agents. Our focus is on rational decision-
making by such agents, where the circumstances obtaining are such that rationality is
bounded. Control room agents, whether human or non-human, need to reason and act
in a changing environment with only limited information available to them. Determining
the current state of the environment is a central concern for control room agents if they
are to reason and act sensibly. A control room agent cannot plan its actions without
having an internal representation (epistemic state) of its environment, and cannot make
rational decisions unless this representation, to some level of accuracy, reflects the state
of its environment. The focus of this thesis is on three aspects regarding the epistemic
functioning of a control room agent:
1. How should the epistemic state of a control room agent be represented in order to
facilitate logical analysis?
2. How should a control room agent change its epistemic state upon receiving new
information?
3. How should a control room agent combine available information from different
sources?
In describing the class of control room agents as first-order intentional systems hav-
ing both informational and motivational attitudes, an agent-oriented view is adopted.
The central construct used in the information-theoretic approach, which is qualitative in
nature, is the concept of a templated ordering.
Representing the epistemic state of a control room agent by a (special form of) tem-
plated ordering signals a departure from the many approaches in which only the beliefs
of an agent are represented. Templated orderings allow for the representation of both
knowledge and belief.
A control room agent changes its epistemic state according to a proposed epistemic
change algorithm, which allows the agent to select between two well-established forms of
belief change operations, namely, belief revision and belief update.
The combination of (possibly conflicting) information from different sources has re-
ceived a lot of attention in recent years. Using templated orderings for the semantic
representation of information, a new family of purely qualitative merging operations is
developed.School of ComputingPh. D. (Computer Science