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In-Depth Information
Within the context of argumentation, an approach that is related to underlying inter-
ests is
value-based argumentation
[9,10]. Values are used in the sense of 'fundamental
social or personal goods that are desirable in themselves' [10], and are used as the
basis for persuasive argument in practical reasoning. In value-based argumentation, ar-
guments are associated with values that they promote. Values are ordered according to
importance to a particular audience. An argument only defeats another argument if it
attacks it and the value promoted by the attacked argument is not more important than
the value promoted by the attacker. We will illustrate this with a little example. Con-
sider two job offers
a
and
b
.
a
offers a higher salary, but
b
offers a better position. We
can construct two mutually attacking preference arguments,
A
: 'I prefer job offer
a
over
job offer
b
because it has a higher salary', and
B
: 'I prefer job offer
b
over job offer
a
because it has a better position'. In Dung-style argumentation frameworks [11], there is
no way to choose between two mutually attacking arguments (unless one is defended
and the other is not). In value-based argumentation, we could say that preferring
a
over
b
promotes the value of wealth (
w
), and preferring
b
over
a
promotes the value of status
(
s
), and e.g. wealth is considered more important than status. In this case
A
defeats
B
,
but not the other way around.
In this framework, every argument is associated with only one value, while in
many cases there are multiple values or interests at stake. [12] define so-called
value-
specification argumentation frameworks
, in which arguments can support multiple
values, and preference statements about values can be given. However, the preference
between arguments is not derived from the preference between the values promoted by
the arguments. Besides, there is no guarantee that a value-specification argumentation
framework is consistent, i.e., some sets of preference statements do not correspond to a
preference ordering on arguments.
In value-based argumentation, we cannot argue about what values are promoted by
the arguments or the ordering of values; this mapping and ordering are supposed to
be given. But these might well be the conclusion of reasoning, and might be defeasi-
ble. Therefore, it would be natural to include this information at the object level. [13]
describe some argument schemes regarding the influence of certain perspectives on val-
ues. However, for the aggregation of multiple values, they assume a given order on sets
of values, whereas we want to derive such an order from an order on individual values.
4
Qualitative Multi-criteria Preferences
Regardless of whether we take issues or interests as criteria, we need to be able to
model multiple criteria. In any realistic setting, preferences are determined by multiple
criteria and the interplay between them. Therefore we shortly introduce two well-known
approaches to multi-criteria preferences which we will use in our framework.
One approach is
ceteris paribus
('all else being equal') comparison. One outcome is
preferred to another ceteris paribus, if it is better on some criteria and the same on all
other criteria. This approach has been widely used since [14]. Also [15] derive prefer-
ences from sets of goals in a ceteris paribus way. In [16], ceteris paribus comparison is
combined with conditional preferences in a graphical preference language called CP-
nets. The preference order resulting from ceteris paribus comparison is not complete; an
