Pere Pardo

JAIR Journal 2024 Journal Article

The Goal after Tomorrow: Offline Goal Reasoning with Norms

• Pere Pardo
• Christian Strasser

Recent studies have focused on autonomous agents that select their own goals and then select actions to achieve these goals, using online Goal Reasoning (GR). GR agents can revise goals and plans at execution time if unexpected outcomes occur. However, for ethical or legal agent design, even the partial execution of an online plan may result in foreseeable norm violations. To prevent these violations, it is crucial to incorporate GR already at the planning phase. To this end, we design an offline GR system that can harbour normative systems or deontic logics for goal generation. Our main results include a characterization and comparison of the completeness classes for a variety of offline GR planners, and a discussion of the irreducibility of offline GR to pure planning methods.

JAIR Journal 2023 Journal Article

The Jiminy Advisor: Moral Agreements among Stakeholders Based on Norms and Argumentation

• Beishui Liao
• Pere Pardo
• Marija Slavkovik
• Leendert van der Torre

An autonomous system is constructed by a manufacturer, operates in a society subject to norms and laws, and interacts with end users. All of these actors are stakeholders affected by the behavior of the autonomous system. We address the challenge of how the ethical views of such stakeholders can be integrated in the behavior of an autonomous system. We propose an ethical recommendation component called Jiminy which uses techniques from normative systems and formal argumentation to reach moral agreements among stakeholders. A Jiminy represents the ethical views of each stakeholder by using normative systems, and has three ways of resolving moral dilemmas that involve the opinions of the stakeholders. First, the Jiminy considers how the arguments of the stakeholders relate to one another, which may already resolve the dilemma. Secondly, the Jiminy combines the normative systems of the stakeholders such that the combined expertise of the stakeholders may resolve the dilemma. Thirdly, and only if these two other methods have failed, the Jiminy uses context-sensitive rules to decide which of the stakeholders take preference over the others. At the abstract level, these three methods are characterized by adding arguments, adding attacks between arguments, and revising attacks between arguments. We show how a Jiminy can be used not only for ethical reasoning and collaborative decision-making, but also to provide explanations about ethical behavior.

FLAP Journal 2019 Journal Article

Strengthening Gossip Protocols using Protocol-Dependent Knowledge.

• Hans van Ditmarsch
• Malvin Gattinger
• Louwe B. Kuijer
• Pere Pardo

Distributed dynamic gossip is a generalization of the classic telephone problem in which agents communicate to share secrets, with the additional twist that also telephone numbers are exchanged to determine who can call whom. Recent work focused on the success conditions of simple protocols such as “Learn New Secrets” (LNS) wherein an agent a may only call another agent b if a does not know b’s secret. A protocol execution is successful if all agents get to know all secrets. On partial networks these protocols sometimes fail because they ignore information available to the agents that would allow for better coordination. We study how epistemic protocols for dynamic gossip can be strengthened, using epistemic logic as a simple protocol language with a new operator for protocol-dependent knowledge. We provide definitions of different strengthenings and show that they perform better than LNS, but we also prove that there is no strengthening of LNS that always terminates successfully. Together, this gives us a better picture of when and how epistemic coordination can help in the dynamic gossip problem in particular and distributed systems in general.

FLAP Journal 2018 Journal Article

Argument Strength in Formal Argumentation.

• Mathieu Beirlaen
• Jesse Heyninck
• Pere Pardo
• Christian Straßer

FLAP Journal 2018 Journal Article

Tuning the Program Transformers from CC to PDL.

• Pere Pardo
• Enrique Sarión-Morrillo
• Fernando Soler-Toscano
• Fernando R. Velázquez-Quesada

JELIA Conference 2014 Conference Paper

Efficient Program Transformers for Translating LCC to PDL

• Pere Pardo
• Enrique Sarrión-Morillo
• Fernando Soler-Toscano
• Fernando R. Velázquez-Quesada

Abstract This work proposes an alternative definition of the so-called program transformers, used to obtain reduction axioms in the Logic of Communication and Change. Our proposal uses an elegant matrix treatment of Brzozowski’s equational method instead of Kleene’s translation from finite automata to regular expressions. The two alternatives are shown to be equivalent, with Brzozowski’s method having the advantage of being computationally more efficient.

JELIA Conference 2012 Conference Paper

Extending a Temporal Defeasible Argumentation Framework with Possibilistic Weights

• Lluís Godo
• Enrico Marchioni
• Pere Pardo

Abstract Recently, a temporal extension of the argumentation defeasible reasoning system \(\mbox{\textsf{DeLP}}\) has been proposed. This system, called \(\mbox{\textsf{t-DeLP}}\), allows to reason defeasibly about changes and persistence over time but does not offer the possibility of ranking defeasible rules according to criteria of preference or certainty (in the sense of belief). In this contribution we extend \(\mbox{\textsf{t-DeLP}}\) by allowing to attach uncertainty weights to defeasible temporal rules and hence stratifying the set of defeasible rules in a program. Technically speaking, weights are modelled as necessity degrees within the frame of possibility theory, a qualitative model of uncertainty.

AAMAS Conference 2012 Conference Paper

Planning in the Logics of Communication and Change

• Pere Pardo
• Mehrnoosh Sadrzadeh

We adapt backward planning to Logics of Communication and Change (LCC), that model how do actions, announcements and sensing change facts and agents’ beliefs. An LCC planner takes into account the epistemic effects of planned actions upon other agents, if their beliefs are relevant to her goals. Our results include: a characterization of frame axioms as theorems in ∗-free LCC, and soundness and completeness results for deterministic planning and strong planning in the non-deterministic case.

AAMAS Conference 2011 Conference Paper

Multiagent Argumentation for Cooperative Planning in DeLP-POP

• Pere Pardo
• Sergio Pajares
• Eva Onaindia
• Pilar Dellunde
• Llu
• iacute; s Godo

This contribution proposes a model for argumentation-based multi-agent planning, with a focus on cooperative scenarios. It consists in a multi-agent extension of DeLP-POP, partial order planning on top of argumentation-based defeasible logic programming. In DeLP-POP, actions and arguments (combinations of rules and facts) may be used to enforce some goal, if their conditions (are known to) apply and arguments are not defeated by other arguments applying. In a cooperative planning problem a team of agents share a set of goals but have diverse abilities and beliefs. In order to plan for these goals, agents start a stepwise dialogue consisting of exchanges of plan proposals, plus arguments against them. Since these dialogues instantiate an A search algorithm, these agents will find a solution if some solution exists, and moreover, it will be provably optimal (according to their knowledge).