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1

From Argumentation Frameworks to Voting Systems and Back

Benedetti I., Bistarelli S.

Fundamenta Informaticae

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2017

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Vol. 150, nr 1

25--48

EN

Formal voting theories are established and can be used to determine if a voting system is fair or not in order to preserve democracy. There are a lot of voting systems described in the literature, with several properties, useful in many contexts. The Argumentation Framework is based on the exchange and the evaluation of interacting arguments which may represent information of various kinds. We show that Argumentation Frameworks can be interpreted within a voting theory and considered as voting methods. Using a mapping that associates an argument to a candidate and attacks to votes, we define a bidirectional mapping between the two theories and investigate how fairness criteria defined for voting systems can be re-interpreted within Argumentation Framework. We also show how voting ballots can be seen as suitable semantics for Argumentation Frameworks.

2

A Comparative Test on the Enumeration of Extensions in Abstract Argumentation

Bistarelli S., Rossi F., Santini F.

Fundamenta Informaticae

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2015

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Vol. 140, nr 3/4

263--278

EN

We compare four different implementations of reasoning-tools dedicated to Abstract Argumentation Frameworks. These systems are ArgTools, ASPARTIX, ConArg2, and Dung-O-Matic. They have been tested over three different models of randomly-generated graph models, corresponding to the Erdös-Rényi model, the Kleinberg small-world model, and the scale-free Barabasi-Albert model. This first comparison is useful to study the behaviour of these tools over networks with different topologies (also small-world): we scale the number of arguments to check the limits of today’s systems. Such results can be used to guide further improvements of ConArg2 (our tool), but also different tools.

3

A Secure Non-monotonic Soft Concurrent Constraint Language

Bistarelli S., Santini F.

Fundamenta Informaticae

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2014

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Vol. 134, nr 3/4

261--285

EN

We present a fine-grained security model to enforce the access control on the shared constraint store in Concurrent Constraint Programming (CCP) languages. We show the model for a non-monotonic version of Soft CCP (SCCP), that is an extension of CCP where the constraints have a preference level associated with them. Crisp constraints can be modeled in the same framework as well. In the considered non-monotonic soft version (NmSCCP), it is also possible to remove constraints from the store. The language can be used for coordinating agents on a common store of information that represents the set of shared resources. In such scenarios, it is clearly important to enforce the integrity and confidentiality rights on the resources, in order, for instance, to hide part of the information to some agents, or to prevent an agent to consume too many resources. Finally, we present a bisimulation relation to check equivalence between two programs written in this language.

4

Coalitions of Arguments : An Approach with Constraint Programming

Bistarelli S., Santini F.

Fundamenta Informaticae

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2013

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Vol. 124, nr 4

383--401

EN

The aggregation of generic items into coalitions leads to the creation of sets of homogenous entities. In this paper we accomplish this for an input set of arguments, and the result is a partition according to distinct lines of thought, i.e., groups of 'coherent' ideas. We extend Dung's Argumentation Framework (AF) in order to deal with coalitions of arguments. The initial set of arguments is partitioned into not-intersected subsets. All the found coalitions show the same property inherited by Dung, e.g., all the coalitions in the partition are admissible (or conflict-free, complete, stable): they are generated according to Dung's principles. Each of these coalitions can be assigned to a different agent. We use Soft Constraint Programming as a formal approach to model and solve such partitions in weighted AFs: semiring algebraic structures can be used to model different optimization criteria for the obtained coalitions. Moreover, we implement and solve the presented problem with JaCoP, a Java constraint solver, and we test the code over a small-world network.

5

Solving Distributed CSPs Probabilistically

Bistarelli S., Gosti G.

Fundamenta Informaticae

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2011

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Vol. 105, nr 1/2

57-78

EN

Constraint solving problems (CSPs) are the formalization of a large range of problems that emerge fromcomputer science. The solving methodology described here is based on the naming game. The two main features that distinguish this methodology from most distributed constraint solving problem (DCSPs) methods are: the system can react to small instance changes, and it does not require pre-agreed agent/variable ordering. The naming game was introduced to represent N agents that have to bootstrap an agreement on a name to give to an object. The agents do not have a hierarchy, and use a minimal protocol. Still they converge to a consistent state by using a distributed strategy. For this reason, the naming game can be used to untangle DCSPs. It was shown that a distributed system of uniform finite state machines does not solve the ring ordering problem in all the algorithm executions. Our algorithm is a distributed uniform system of agents able to perform random decisions when presented with equivalent alternatives. We show that this algorithm solves the ring ordering problem with a probability one.

6

A Nonmonotonic Soft Concurrent Constraint Language to Model the Negotiation Process

Bistarelli S., Santini F.

Fundamenta Informaticae

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2011

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Vol. 111, nr 3

257-279

EN

We present an extension of the Soft Concurrent Constraint language that allows the nonmonotonic evolution of the constraint store. To accomplish this, we introduce some new operations: retract(c) reduces the current store by c, updateX(c) transactionally relaxes all the constraints of the store that deal with the variables in the set X, and then adds a constraint c; nask(c) tests if c is not entailed by the store. The new retraction operators also permit to reason about Belief Revision, i.e. the process of changing beliefs to take into account a new piece of information. We present this framework as a possible solution to the negotiation of resources (e.g. web services and network resource allocation) that need a given Quality of Service (QoS). For this reason we also show the the new operators of the language satisfy the Belief Revision postulates [20], which can be used in the negotiation process. The QoS requirements (expressed as semiring levels) of all the parties should converge on a formal agreement through a negotiation process, which specifies the contract that must be enforced.