Abstract-Band - Fakultät für Informatik, TU Wien - Technische ...

Thomas Linsbichler
On the Limits of Expressiveness in Abstract Argumentation Semantics:
Realizability and Signatures
Studium: Masterstudium Computational Intelligence
BetreuerIn: Privatdoz. Dr. Stefan Woltran
In recent years the research field of argumentation, in particular the formal
approach of abstract argumentation introduced by Dung, has become a major
topic in the study of AI. A so-called abstract argumentation framework is a
directed graph where nodes represent arguments and arrows represent conflicts
between arguments. The question of which arguments can be accepted
out of an argumentation framework, called extension-sets, is answered by
argumentation semantics. Surprisingly, a systematic comparison of their capability
in terms of multiple extensions has been neglected so far. Understanding
which extensions can, in principle, go together when a framework is evaluated
with respect to a semantics of interest not only clarifies the "strength" of that
semantics but also is a crucial issue in several applications. The aim of the
master's thesis is to study the expressiveness of the naive, stage, stable, preferred,
semi-stable, and complete semantics, by characterizing their signatures.
The signature of a semantics is defined as the set of all possible sets of extensions
one can obtain from the semantics, given an arbitrary argumentation
framework. For each semantics we give necessary conditions for an extensionset
to be in the signature, i.e. properties which are fulfilled by the outcomes of
the semantics for each framework, as well as (corresponding) sufficient conditions
for an extension-set to be in the signature, which make the extensionset
realizable under the semantics. The thesis provides constructions of argumentation
frameworks realizing extension-sets under the various semantics.
The characterizations of the signatures of the semantics give rise to a
systematic comparison of their expressiveness. We show that, with one exception,
all semantics we deal with possess different levels of expressiveness.
Finally the thesis investigates strict realizability, i.e. realizing an extension-set
by a framework by not using additional arguments.
Johannes Maschler
Data Exchange of Relational Data and Beyond
Studium: Masterstudium Software Engineering & Internet Computing
BetreuerIn: Univ.Prof. Dr. Reinhard Pichler
Data exchange has been a very active area of database research over the past
decade. In the first place, data exchange of relational data has been investigated.
More recently, data exchange research has been extended to other data
models such as knowledge bases and XML. The goal of this thesis is to
summarize the state of the art in data exchange. We thus compare the results
for the main problems in data exchange of relational data, knowledge bases,
and XML data.
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