Talks

In this talk, I discussed various tools developed for and by the ComSoC community. I began by highlighting recent developments in PrefLib. Subsequently, I provided an overview of the general ComSoC ecosystem, with a particular emphasis on newly created tools. Finally, I proposed a general discussion on organizing and valorizing such tools.

We introduce a family of normative principles to assess fairness in the context of participatory budgeting. These principles are based on the fundamental idea that budget allocations should be fair in terms of the resources invested into meeting the wishes of individual voters. This is in contrast to earlier proposals that are based on specific assumptions regarding the satisfaction of voters with a given budget allocation. We analyze these new principles in axiomatic, algorithmic, and experimental terms.

This is a longer version of the talk on the paper with the same name that was already presented at IJCAI 2022. We study settings in which agents with incomplete preferences need to make a collective decision. We focus on a process of majority dynamics where issues are addressed one at a time and undecided agents follow the opinion of the majority. We assess the effects of this process on various consensus notions—such as the Condorcet winner—and show that in the worst case, myopic adherence to the majority damages existing consensus; yet, simulation experiments indicate that the damage is often mild. We also examine scenarios where the chair of the decision process can control the existence (or the identity) of consensus, by determining the order in which the issues are discussed.

When seeking for suitable mechanisms for participatory budgeting (PB), one has to decide on which criteria to assess them. In this paper, I present several appealing criteria for PB mechanisms. I briefly introduce each of them and discuss their impact on the design of PB mechanisms.

We study settings in which agents with incomplete preferences need to make a collective decision. We focus on a process of majority dynamics where issues are addressed one at a time and undecided agents follow the opinion of the majority. We assess the effects of this process on various consensus notions—such as the Condorcet winner—and show that in the worst case, myopic adherence to the majority damages existing consensus; yet, simulation experiments indicate that the damage is often mild. We also examine scenarios where the chair of the decision process can control the existence (or the identity) of consensus, by determining the order in which the issues are discussed.

We introduce a new family of normative principles for fairness in participatory budgeting. These principles are based on the fundamental idea that budget allocations should be fair in terms of the effort invested into meeting the wishes of each voter. This is in contrast to earlier proposals that instead are based on specific assumptions about the satisfaction voters with a given budget allocation. We analyze these new principles in axiomatic, algorithmic, and experimental terms.

We study a model for fair division in which agents, aside from getting allocated a bundle of items (that can include both goods and chores), are also to be assigned a position on a social graph. We focus on the local variant of natural fairness criteria: local envy-freeness, local envy-freeness up to one item and local proportionality. For each criterion, we study the computational complexity of the task of producing a fair position assignment and, possibly also an item allocation. Specifically, we focus on how different graph topologies influence the complexity of these problems. In many cases both tasks prove to be intractable for the criteria that we consider. Then, we consider the parameterized complexity of the problem. We show how the problem is equivalent to the known dichotomy conjecture for the parameterized graph embedding problem. Thus, we focus on tree-like graphs, and prove fixed-parameter tractability for all criteria but local proportionality, using a set of parameters that are, under some assumptions, reasonably small.

When seeking for suitable mechanisms for participatory budgeting, one has to decide on which criteria to assess them. In this talk, I briefly present several appealing criteria for PB mechanisms. I introduce each of them and discuss their impact on the design of PB mechanisms.

In this talk I present a recent work with Jan Maly, Ulle Endriss and Martin Lackner. We introduce a new family of normative principles for fairness in participatory budgeting. These principles are based on the fundamental idea that budget allocations should be fair in terms of the effort invested into meeting the wishes of each voter. This is in contrast to earlier proposals that instead are based on specific assumptions about the satisfaction voters with a given budget allocation. We analyze these new principles in axiomatic and algorithmic terms.

In this talk I will discuss several recent papers on the topic of participatory budgeting. Participatory budgeting is usually studied as an extension of multi-winner voting, where selecting a candidate results in paying a cost, and where a budget limit constrains the cost of the selected candidates. Although highly relevant for the technical analysis, this approach does not fully capture participatory budgeting processes as they happen in real l ife. This talk aims at presenting other models for participatory budgeting that more closely resemble these real-life processes. We will discuss the idea of a two-stage model where agents first propose some projects and then vote over the shortlisted projects. We will also have a look at what changes when the process is repeated over several years. Finally, we will have a look at how to include additional constraints on top of the budget limit: quotas over categories of projects, dependencies between the projects, ...

When seeking for suitable mechanisms for participatory budgeting, one has to decide on which criteria to assess them. In this talk, I briefly present several appealing criteria for PB mechanisms. I introduce each of them and discuss their impact on the design of PB mechanisms.

The buurtbudget, known as participatory budgeting in English, is a democratic process aiming at involving citizens in public spending decisions. In several neighborhoods of Amsterdam, residents already can vote for community-driven projects to be paid for from public funds. However, organizing this process is not straightforward, especially when it comes to making a decision based on the ballots that have been submitted. During this talk, we will see why some natural procedures to determine the winning projects suffer some drawbacks and how to circumvent those drawbacks.

This talk presents the paper "Designing Participatory Budgeting Mechanisms Grounded in Judgment Aggregation" that was published at KR-2020. We prepared a lightened version for COMSOC-2021, focusing more on the COMSOC parts of this work (compared to the KR version).

In this talk I will give a general overview of the epistemic approach in computational social choice. In this body of literature, voting is seen as a mechanism to recover the objectively best outcome for the society, given noisy votes. I will discuss the general framework as well as some selected recent contributions, reviewing the main concepts used in the literature.

We introduce a new approach for designing rules for participatory budgeting, the problem of deciding on the use of public funds based directly on the views expressed by the citizens concerned. The core idea is to embed instances of the participatory budgeting problem into judgment aggregation, a powerful general-purpose framework for modelling collective decision making. Taking advantage of the possibilities offered by judgment aggregation, we enrich the familiar setting of participatory budgeting with additional constraints, namely dependencies between projects and quotas regarding different types of projects. We analyze the rules obtained both in algorithmic and in axiomatic terms.

Participatory Budgeting is a growing topic in social choice. Introduced in the late 1980s in Brazil, it is now viewed as a critical topic to improve the democratic process. In this talk I introduced the concept of Participatory Budgeting and gave an overview of the related literature in the field of Computational Social Choice.

In this talk I presented some recent work I have been doing with Haris Aziz. We consider a multiagent resource allocation setting in which an agent's utility may decrease or increase when an item is allocated. We present stronger and relaxed versions of the group envy-freeness concept that are especially suitable for the allocation of indivisible items. Of particular interest is a concept called group envy-freeness up to one item (GEF1). We studied which fairness concepts guarantee the existence of a fair allocation under which preference domain. For two natural classes of additive utilities, we designed polynomial-time algorithms to compute a GEF1 allocation.

This is a presentation of the work we did with Davide Grossi when I was visiting him in Groningen. It was presented during the Syntax Meets Semantics conference in Amsterdam. A paper was published at AAMAS 2019 on this work.