Luca Gasparini

Severity-Sensitive Robustness Analysis in Normative Systems

Norms specify ideal behaviour. Agents, however, are autonomous, and may fail to comply with the ideal. Contrary to Duty obligations can be used to specify reparational behaviour that mitigates the effects of a violation. In addition to specifying reparational behaviours, it is important to understand how robust a system is against possible violations. Depending on what kind of system property we want to preserve, non-compliance with different norms may be of varying severity. We propose a method for analysing robustness of normative systems, with support for Contrary to Duty obligations. We introduce violation severity as a concept orthogonal to reparational behaviour and specify it by means of a partial order over norms. We use this severity partial order, together with normative specifications, to rank the possible worlds from the most to the least compliant. In this way, we are able to use model checking to analyse robustness to a certain severity, or whether it is possible to achieve a certain goal, without violating any norm of a given severity.

Severity-sensitive norm-governed multi-agent planning

In making practical decisions, agents are expected to comply with ideals of behaviour, or norms. In reality, it may not be possible for an individual, or a team of agents, to be fully compliant—actual behaviour often differs from the ideal. The question we address in this paper is how we can design agents that act in such a way that they select collective strategies to avoid more critical failures (norm violations), and mitigate the effects of violations that do occur. We model the normative requirements of a system through contrary-to-duty obligations and violation severity levels, and propose a novel multi-agent planning mechanism based on Decentralised POMDPs that uses a qualitative reward function to capture levels of compliance: N-Dec-POMDPs. We develop mechanisms for solving this type of multi-agent planning problem and show, through empirical analysis, that joint policies generated are equally as good as those produced through existing methods but with significant reductions in execution time.

Norm analysis and norm-governed planning

This software package contains the implementation of the following algorithms: (1) a method to compute a preference relation given a set of norms with contrary-to-duty structures and partial order over violation severity; (2) the Dec-POMDP and N-Dec-POMDP multi-agent planners that can work with a qualitative reward function, representing a preference relation; and (3) a parser and reasoner for the COIR normative language (optional). The license for the use of this software is based on BSD, and a free commercial license is available; details provided in the source code. Please see the README.txt file for further information. CRC32 checksum for this file is F1440475 File size: 96669676 Bytes

Observation-based multi-agent planning with communication

Models of decentralized online planning vary in the information that individual agents use to make local action decisions. Some models consider only local observations, eschewing coordination through communication. Others use communication to ensure that all agents are aware of the action decisions of others, but assume costless and delay-free communication. In this paper, we propose a model of online planning (OB-MAP) that uses estimates of the value of communicating to manage coordination through communication as costs vary. We compare this approach to existing models in widely employed benchmark problems, demonstrating that OB-MAP performs significantly better in many scenarios regardless of varying (including infinite) cost of communication.

CÒIR: verifying normative specifications of complex systems

Existing approaches for the verification of normative systems consider limited representations of norms, often neglecting collective imperatives, deadlines and contrary-to-duty obligations. In order to capture the requirements of real-world scenarios, these structures are important. In this paper we propose methods for the specification and formal verification of complex normative systems that include contrary-to-duty, collective and event-driven imperatives with deadlines. We propose an operational syntax and semantics for the specification of such systems. Using Maude and its linear temporal logic model checker, we show how important properties can be verified for such systems, and provide some experimental results for both bounded and unbounded verification.