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Holger Billhardt

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17 papers
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17

JAAMAS Journal 2026 Journal Article

Learning the value systems of agents with preference-based and inverse reinforcement learning

  • Andrés Holgado-Sánchez
  • Holger Billhardt
  • Sascha Ossowski

Abstract Agreement Technologies refer to open computer systems in which autonomous software agents interact with one another, typically on behalf of humans, in order to come to mutually acceptable agreements. With the advance of AI systems in recent years, it has become apparent that such agreements, in order to be acceptable to the involved parties, must remain aligned with ethical principles and moral values. However, this is notoriously difficult to ensure, especially as different human users (and their software agents) may hold different value systems, i. e. they may differently weigh the importance of individual moral values. Furthermore, it is often hard to specify the precise meaning of a value in a particular context in a computational manner. Methods to estimate value systems based on human-engineered specifications, e. g. based on value surveys, are limited in scale due to the need for intense human moderation. In this article, we propose a novel method to automatically learn value systems from observations and human demonstrations. In particular, we propose a formal model of the value system learning problem, its instantiation to sequential decision-making domains based on multi-objective Markov decision processes, as well as tailored preference-based and inverse reinforcement learning algorithms to infer value grounding functions and value systems. The approach is illustrated and evaluated by two simulated use cases.

AAMAS Conference 2026 Conference Paper

Learning the Value Systems of Societies with Preference-based Multi-objective Reinforcement Learning

  • Andrés Holgado-Sánchez
  • Peter Vamplew
  • Richard Dazeley
  • Sascha Ossowski
  • Holger Billhardt

Value-aware AI should recognise human values and adapt to the value systems (value-based preferences) of different users. This requires acquiring computable representations of values, a process that can be prone to misspecification. The social nature of values demands their representation to adhere to multiple users while value systems are diverse, yet exhibit patterns among groups. In sequential decision making, efforts have been made towards personalization for different goals or values from demonstrations of diverse agents. However, these approaches demand manually designed features or lack value-based interpretability and/or adaptability to diverse user preferences. We propose algorithms for learning models of value alignment and value systems for a society of agents in Markov Decision Processes (MDPs), based on clustering and preference-based multiobjectivereinforcementlearning(PbMORL). Wejointlylearnsociallyderived value alignment models (groundings) and a set of value systems that concisely represent different groups of users (clusters) in a society. Each cluster consists of a value system representing the value-based preferences of its members and an approximately Pareto-optimal policy that reflects behaviours aligned with this value system. We evaluate our method against a state-of-the-art PbMORL algorithm and baselines on two MDPs with human values.

ICRA Conference 2025 Conference Paper

Capacitated Agriculture Fleet Vehicle Routing with Implements and Limited Autonomy: A Model and a Two-Phase Solution Approach

  • Aitor López Sánchez
  • Marin Lujak
  • Frédéric Semet
  • Holger Billhardt

In this paper, we study the vehicle routing problem (VRP) for a fleet of cooperative autonomous agricultural robots (agribots) equipped with detachable implements, with the goal of efficiently and sustainably completing agricultural tasks in precision crop farming. State of the art in the area of agribot fleet routing with detachable implements is lacking. Consequently, we propose the Capacitated Agriculture Fleet Vehicle Routing Problem with Implements and Limited Autonomy (CAFVRPILA), designed to optimize the agribot fleet's routes across a set of given agricultural tasks while considering implement capacities, agribot-implement compatibilities, and agribots' limited battery autonomies. A heuristic two-phase decomposition approach is proposed for this problem. Simulation experiments show that minimizing travel distances and costs with CAFVRPILA enhances sustainable farming while maximizing productivity and resource use. The results also demonstrate that synchronizing multiple operations improves efficiency, particularly in larger fleets.

ECAI Conference 2025 Conference Paper

Learning the Value Systems of Societies from Preferences

  • Andrés Holgado-Sánchez
  • Holger Billhardt
  • Sascha Ossowski
  • Sara Degli-Esposti

Aligning AI systems with human values and the value-based preferences of various stakeholders (their value systems) is key in ethical AI. In value-aware AI systems, decision-making draws upon explicit computational representations of individual values (groundings) and their aggregation into value systems. As these are notoriously difficult to elicit and calibrate manually, value learning approaches aim to automatically derive computational models of an agent’s values and value system from demonstrations of human behaviour. Nonetheless, social science and humanities literature suggest that it is more adequate to conceive the value system of a society as a set of value systems of different groups, rather than as the simple aggregation of individual value systems. Accordingly, here we formalize the problem of learning the value systems of societies and propose a method to address it based on heuristic deep clustering. The method learns socially shared value groundings and a set of diverse value systems representing a given society by observing qualitative value-based preferences from a sample of agents. We evaluate the proposal in a use case with real data about travelling decisions.

AILAW Journal 2019 Journal Article

Legal and ethical implications of applications based on agreement technologies: the case of auction-based road intersections

  • José-Antonio Santos
  • Alberto Fernández
  • Mar Moreno-Rebato
  • Holger Billhardt
  • José-A. Rodríguez-García
  • Sascha Ossowski

Abstract Agreement technologies refer to a novel paradigm for the construction of distributed intelligent systems, where autonomous software agents negotiate to reach agreements on behalf of their human users. Smart Cities are a key application domain for agreement technologies. While several proofs of concept and prototypes exist, such systems are still far from ready for being deployed in the real-world. In this paper we focus on a novel method for managing elements of smart road infrastructures of the future, namely the case of auction-based road intersections. We show that, even though the key technological elements for such methods are already available, there are multiple non-technical issues that need to be tackled before they can be applied in practice. For this purpose, we analyse legal and ethical implications of auction-based road intersections in the context of international regulations and from the standpoint of the Spanish legislation. From this exercise, we extract a set of required modifications, of both technical and legal nature, which need to be addressed so as to pave the way for the potential real-world deployment of such systems in a future that may not be too far away.

EUMAS Conference 2017 Conference Paper

An Ontology for Sharing Touristic Information

  • Carmen Fernández
  • Alberto Fernández 0002
  • Holger Billhardt

Abstract E-Tourism applications require reliable means for sharing and reusing information and the possibility to add intelligence and inferred knowledge. In this paper, we focus on developing an ontology or common vocabulary for the tourism domain and, in particular, to represent resources from Croatia. We evaluate some of the most popular ontology development methodologies for this case. As a result of this assessment we present a proposal for a methodology that combines activities from both traditional and simplified methods.

EUMAS Conference 2016 Conference Paper

A Proposal for Situation-Aware Evacuation Guidance Based on Semantic Technologies

  • Holger Billhardt
  • Jürgen Dunkel
  • Alberto Fernández 0002
  • Marin Lujak
  • Ramón Hermoso
  • Sascha Ossowski

Abstract Smart Cities require reliable means for managing installations that offer essential services to the citizens. In this paper we focus on the problem of evacuation of smart buildings in case of emergencies. In particular, we present a proposal for an evacuation guidance system that provides individualized evacuation support to people in case of emergencies. The system uses sensor technologies and Complex Event Processing to obtain information about the current situation of a building in each moment. Using semantic Web technologies, this information is merged with static knowledge (special user characteristics, building topology, evacuation knowledge) in order to determine (and dynamically update) the most appropriate individualized evacuation routes for each user.

EUMAS Conference 2015 Conference Paper

Towards Smart Open Dynamic Fleets

  • Holger Billhardt
  • Alberto Fernández 0002
  • Marin Lujak
  • Sascha Ossowski
  • Vicente Julián
  • Juan Francisco de Paz
  • Josefa Z. Hernández

Abstract Nowadays, vehicles of modern fleets are endowed with advanced devices that allow the operators of a control center to have global knowledge about fleet status, including existing incidents. Fleet management systems support real-time decision making at the control center so as to maximize fleet performance. In this paper, setting out from our experience in dynamic coordination of fleet management systems, we focus on fleets that are open, dynamic and highly autonomous. Furthermore, we propose how to cope with the scalability problem as the number of vehicles grows. We present our proposed architecture for open fleet management systems and use the case of taxi services as example of our proposal.

IS Journal 2014 Journal Article

Dynamic Coordination in Fleet Management Systems: Toward Smart Cyber Fleets

  • Holger Billhardt
  • Alberto Fernández
  • Lissette Lemus
  • Marin Lujak
  • Nardine Osman
  • Sascha Ossowski
  • Carles Sierra

Fleet management systems are commonly used to coordinate mobility and delivery services in a broad variety of domains. However, their traditional top-down control architecture becomes a bottleneck in open and dynamic environments, where scalability, proactiveness, and autonomy are becoming key factors for their success. Here, the authors present an abstract event-based architecture for fleet management systems that supports tailoring dynamic control regimes for coordinating fleet vehicles, and illustrate it for the case of medical emergency management. Then, they go one step ahead in the transition toward automatic or driverless fleets, by conceiving fleet management systems in terms of cyber-physical systems, and putting forward the notion of cyber fleets.

EUMAS Conference 2014 Conference Paper

Optimizing Emergency Medical Assistance Coordination in After-Hours Urgent Surgery Patients

  • Marin Lujak
  • Holger Billhardt
  • Sascha Ossowski

Abstract This paper treats the coordination of Emergency Medical Assistance (EMA) and hospitals for after-hours surgeries of urgent patients arriving by ambulance. A standard hospital approach during night-shifts is to have standby surgery teams come to hospital after alert to cover urgent cases that cannot be covered by the in-house surgery teams. This approach results in a considerable decrease in staffing costs in respect to having sufficient permanent in-house staff. Therefore, coordinating EMA and the hospitals in a region with their outhouse staff with the objective to have as fast urgent surgery treatments as possible with minimized cost is a crucial parameter of the medical system efficiency and as such deserves a thorough investigation. In practice, the process is manual and the process management is case-specific, with great load on human phone communication. In this paper, we propose a decision support system for the automated coordination of hospitals, surgery teams on standby from home, and ambulances to decrease the time to surgery of urgent patients. The efficiency of the proposed model is proven over simulation experiments.

EAAI Journal 2013 Journal Article

Persuading agents to act in the right way: An incentive-based approach

  • Roberto Centeno
  • Holger Billhardt
  • Ramón Hermoso

Organisational abstractions have been presented during the last years as common solutions to regulate Open MultiAgent Systems. In particular, the concept of norm is defined at design time to assure the correct behaviour of agents in such systems. However, in many cases, the performance of a system does not only depend on the correct behaviour of the agents according to the imposed norms but also on some other efficiency measures. To tackle this issue, this paper puts forward a novel mechanism that attempts to persuade agents to act according to system's preferences. This mechanism relies on incentive policies that aim to induce (not enforce) agents to perform those actions that are more appropriated from the system's point of view. In particular, two different policies have been presented. On the one hand, a policy that tries to promote the most appropriate action regarding the global utility of the system, by assigning a positive incentive to it. On the other hand, a policy that assigns incentives to all actions an agent can choose in a given state, with the aim of persuading the former to choose a “good” action. Besides, incentives are adapted and defined for each individual agent and contextualised by taking into account the state of the system. This task is carried out through a learning process based on Q-learning. Finally, a p2p file sharing scenario has been chosen to validate our approach.

AAMAS Conference 2011 Conference Paper

Adaptive Regulation of Open MAS: an Incentive Mechanism based on Modifications of the Environment

  • Roberto Centeno
  • Holger Billhardt

The global objective of open multiagent systems might be in conflict with individual preferences of rational agents participating in such systems. Addressing this problem, we propose a mechanism able to attach incentives to agent actions such that the global utility of the system is improved. Such incentives are dynamically adjusted to each agent's preferences by using institutional agents called incentivators.

IJCAI Conference 2011 Conference Paper

Using Incentive Mechanisms for an Adaptive Regulation of Open Multi-Agent Systems

  • Roberto Centeno
  • Holger Billhardt

In this paper we propose a mechanism that encourages agents, participating in an open MAS, to follow a desirable behaviour, by introducing modifications in the environment. This mechanism is deployed by using an infrastructure based on institutional agents called incentivators. Each external agent is assigned to an incentivator that is able to discover its preferences, and to learn the suitable modifications in the environment, in order to improve the global utility of a system in response to inadequate design or changes in the population of participating agents. The mechanism is evaluated in a p2p scenario.

ECAI Conference 2010 Conference Paper

Reasoning about Norm Compliance with Rational Agents

  • Moser Silva Fagundes
  • Holger Billhardt
  • Sascha Ossowski

This paper presents a model for rational self-interested agents, which takes into account the possibility of violating norms. The transgressions take place when the expected rewards obtained with the defection from the norms surpass the expected rewards obtained by being norm-compliant. To develop such model, we employ Markov Decision Processes (MDPs). Our approach consists of representing the reactions for norm violations within the MDPs in such a way that the agent is able to reason about how those violations affect her expected utilities and future options.

AAMAS Conference 2010 Conference Paper

Role Evolution in Open Multi-Agent Systems as an Information Source for Trust

  • Ram
  • oacute; n Hermoso
  • Holger Billhardt
  • Sascha Ossowski

In Open Multi-Agent Systems (OMAS), deciding with whom to interact is a particularly difficult task for an agent, as repeated interactions with the same agents are scarce, and reputation mechanisms become increasingly unrealiable. In this work, we present a coordination artifact which can be used by agents in an OMAS to take more informed decisions regarding partner selection, and thus to improve their individual utilities. This artifact monitors the interactions in the OMAS, evolves a role taxonomy, and assigns agents to roles based on their observed performance in different types of interactions. this information can be used by agents to better estimate the expected behaviour of potential counterparts in future interactions. We thus highlight the descriptive features of roles, providing expectations of the behaviour of agents in certain types of interactions, rather than their normative facets. We empirically show that the use of the artifact helps agents to select better partners for their interactions than selection processes based only on agents' own experience. This is especially significant for agents that are newcomers to the OMAS.

AAMAS Conference 2008 Conference Paper

Extending Virtual Organizations to improve trust mechanisms

  • Ram
  • oacute; n Hermoso
  • Roberto Centeno S
  • aacute; nchez
  • Holger Billhardt
  • Sascha Ossowski

Virtual Organizations (VOs) are becoming an increasingly important research topic in the field of Multi-Agent Systems (MAS). The problem of selecting suitable counterparts to interact with is of particular relevance for agents belonging to a VO. This issue has been extensively investigated, applying probability or cognitive approaches, but very few focus has been given to the use of internal organizational structures and the improvement they can provide. In this paper we analyze how organizational structures can support the agent selection process based an trust mechanisms. Furthermore, we present a way to extend VOs automatically (e. g. , their role taxonomies) by detecting and identifying new roles. We show that such extensions lead to an improvement of the agents’ decisions when employing trust mechanisms that take advantage of organizational structures.

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