Tan, Y-H.
http://repub.eur.nl/ppl/3108/
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RePub, Erasmus University RepositoryThe role of diagnosis and decision theory in normative reasoning
http://repub.eur.nl/pub/517/
Wed, 01 Jan 1997 00:00:01 GMT<div>Torre, L.W.N. van der</div><div>Ramos, P.</div><div>Fiadeiro, J.L.</div><div>Tan, Y-H.</div>
A theory of diagnosis and qualitative decision theory are able to formalize reasoning `with' norms. They are thus different from deontic logic, that formalizes reasoning `about' norms. In this paper, we compare two theories of diagnosis for normative systems: Ramos and Fiadeiro's theory of diagnosis developed for organizational process design and Tan and Van der Torre's theory of diagnosis extended with notions of qualitative decision theory. We observe several similarities.Contextual deontic logic
http://repub.eur.nl/pub/518/
Wed, 01 Jan 1997 00:00:01 GMT<div>Torre, L.W.N. van der</div><div>Tan, Y-H.</div>
In this article we propose contextual deontic logic (CDL). Contextual obligations are written as O(Alpha|Beta\\Gamma), and are to be read as `Alpha should be the case if Beta is the case, unless Gamma is the case'. The unless clause is analogous to the justification in Reiter's default rules. We show how contextual obligations can be used to solve certain aspects of contrary-to-duty paradoxes of dyadic deontic logic.How to model normative behavior in Petri nets
http://repub.eur.nl/pub/512/
Mon, 01 Jan 1996 00:00:01 GMT<div>Raskin, J.-F.</div><div>Tan, Y-H.</div><div>Torre, L.W.N. van der</div>
In this paper, we show how to extend the Petri net formalism to represent different types of behavior, in particular normative behavior. This extension is motivated by the use of Petri nets to model bureaucratic procedures, which contain normative aspects like obligations and permissions. We propose to extend Petri nets with a preference relation, a well-known mechanism from deontic logic to discriminate between ideal and varying sub-ideal states.Cancelling and overshadowing: two types of defeasibility in defeasible deontic logic
http://repub.eur.nl/pub/454/
Sun, 01 Jan 1995 00:00:01 GMT<div>Torre, L.W.N. van der</div><div>Tan, Y-H.</div>
In this paper we give a general analysis of dyadic deontic logics that were introduced in the early seventies to formalize deontic reasoning about subideal behavior. Recently it was observed that they are closely related to non-monotonic logics, theories of diagnosis and decision theories. In particular, we argue that two types of defeasibility must be distinguished in a defeasible deontic logic: overridden defeasibility that formalizes cancelling of an obligation by other conditional obligations and factual defeasibility that formalizes overshadowing of an obligation by a violation. We also show that this distinction is essential for an adequate analysis of notorious `paradoxes' of deontic logic such as the Chisholm and Forrester `Paradoxes'.DefDiode: a diagnostic model for defeasible deontic logic
http://repub.eur.nl/pub/456/
Sun, 01 Jan 1995 00:00:01 GMT<div>Tan, Y-H.</div><div>Torre, L.W.N. van der</div>
There is a fundamental difference between a conditional obligation being violated by a fact, and a conditional obligation being overridden by another conditional obligation. In this paper we propose a multi preference semantics for a defeasible deontic logic that is based on this fundamental difference. The semantics contains one preference relation for ideality, which can be used to formalize deontic `paradoxes' like the Chisholm and Forrester `Paradoxes', and another preference relation for normality, which can be used to formalize exceptions. The interference of the two preference orderings generates new questions about preferential semantics.A proof theory for constructive default logic
http://repub.eur.nl/pub/1465/
Fri, 01 Jan 1993 00:00:01 GMT<div>Tan, Y-H.</div>
We present what we call Constructive Default Logic (CDL) - a default logic in which the
fixed-point definition of extensions is replaced by a constructive definition which yield
so-called constructive extensions. Selection functions are used to represent explicitly
the control of the reasoning process in this default logic. It is well-known that Reiter's
original default logic lacks, in general, a default proof theory. We will show that CDL
does have a default proof theory, and we will also show that this is related to the fact
that CDL has the existence property for constructive extensions and that it also has the
semi-monotonicity property. Furthermore, we will also show that, with respect to some
counter-examples that were suggested by Lukaszewicz, constructive extensions yield more
intuitive conclusions than Reiter's extensions. Hence, constructive default logic does not
only have heuristic advantages over Reiter's default theory from a computational point of
view, but it is also more adequate with respect to knowledge representation.Why Friedman's Non-monotonic Reasoning Defies Hempel's Covering Law Model
http://repub.eur.nl/pub/11716/
Tue, 01 Jan 1991 00:00:01 GMT<div>Janssen, M.C.W.</div><div>Tan, Y-H.</div>
In this paper we will show that Hempel's covering law model can't deal very well with explanations that are based on incomplete knowledge. In particular the symmetry thesis, which is an important aspect of the covering law model, turns out to be problematic for these explanations. We will discuss an example of an electric circuit, which clearly indicates that the symmetry of explanation and prediction does not always hold. It will be argued that an alternative logic for causal explanation is needed. And we will investigate to what extent non-monotonic epistemic logic can provide such an alternative logical framework. Finally we will show that our non-monotonic logical analysis of explanation is not only suitable for simple cases such as the electric circuit, but that it also sheds new light on more controversial causal explanations such as Milton Friedman's explanation of the business cycle.