Arguments in structured argumentation are usually defined as trees, and extensions as sets of such treebased arguments with various properties depending on the particular argumentation semantics. However, these arguments and extensions may have redundancies as well as circularities, which are conceptually and computationally undesirable. Focusing on the specific case of Assumption-Based Argumentation (ABA), we propose novel notions of arguments and admissible/grounded extensions, both defined in terms of graphs. We show that this avoids the redundancies and circularities of standard accounts, and set out the relationship to standard tree-based arguments and admissible/grounded extensions (as sets of arguments). We also define new notions of graph-based admissible/grounded dispute derivations for ABA, for determining whether specific sentences hold under the admissible/grounded semantics. We show that these new derivations are superior with respect to standard dispute derivations in that they are complete in general, rather than solely for restricted classes of ABA frameworks. Finally, we present several experiments comparing the implementation of graph-based admissible/grounded dispute derivations with implementations of standard dispute derivations, suggesting that the graph-based approach is computationally advantageous.
Despite several research studies, the effective analysis of policy based systems remains a significant challenge. Policy analysis should at least (i) be expressive (ii) take account of obligations and authorizations, (iii) include a dynamic system model, and (iv) give useful diagnostic information. We present a logic-based policy analysis framework which satisfies these requirements, showing how many significant policy-related properties can be analysed, and we give details of a prototype implementation.
The paper introduces new developments of the original AREA method.
A rigorous mathematical
proof that the equilibrium points are the only ones which satisfy the
maximum AREA criterion
in the case of a two-component, two-phase system is given for the first
time. A rigorous proof
that the maximum AREA criterion is a necessary but not a sufficient
condition for equilibrium
in the case of an N-component, two-phase system is given
also for the first time in the paper.
Two test examples which reinforce the validity of the theoretical
results obtained are presented
and discussed.
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