No Finite Model Property for Logics of Quantified Announcements

Quantification over public announcements shifts the perspective from reasoning strictly about the results of a particular announcement to reasoning about the existence of an announcement that achieves some certain epistemic goal. Depending on the type of the quantification, we get differ- ent formalisms, the most known of which are arbitrary public announcement logic (APAL), group announcement logic (GAL), and coalition announcement logic (CAL). It has been an open question whether the logics have the finite model property, and in the paper we answer the question negatively. We also discuss how this result is connected to other open questions in the field.publishedVersio

Evidence-Based Beliefs in Many-Valued Modal Logics

Rational agents, humans or otherwise, build their beliefs from evidence – a process which we call consolidation. But how should this process be carried out? In this thesis, we study a multi-agent logic of evidence and the question how agents should form beliefs in this logic. The main contributions of this thesis are twofold. First, we present and study a many-valued modal logic, and show how it can be suitable for modelling multi-agent scenarios where each agent has access to some evidence, which in turn can be processed into beliefs. This is a technical and practical contribution to many-valued modal logics. Second, we open new paths for research in the field of evidence logics: we show a new approach based on many-valued logics, we highlight the concept of consolidations and the importance of looking at their dynamic nature, and build a methodology based on rationality postulates to evaluate them

What will they say?—Public Announcement Games

Dynamic epistemic logic describes the possible information-changingactions available to individual agents, and their knowledge pre- and post conditions.For example, public announcement logic describes actions in the form of public,truthful announcements. However, little research so far has considered describing andanalysing rational choice between such actions, i.e., predictingwhat rational self-interestedagents actually will or should do. Since the outcome of information exchangeultimately depends on the actions chosen by all the agents in the system, and assumingthat agents have preferences over such outcomes, this is a game theoretic scenario.This is, in our opinion, an interesting general research direction, combining logic andgame theory in the study of rational information exchange. In this article we take somefirst steps in this direction: we consider the case where available actions are publicannouncements, and where each agent has a (typically epistemic) goal formula thatshe would like to become true. What will each agent announce? The truth of the goalformula also depends on the announcements made by other agents. We analyse suchpublic announcement games

What will they say?—Public Announcement Games

Dynamic epistemic logic describes the possible information-changingactions available to individual agents, and their knowledge pre- and post conditions.For example, public announcement logic describes actions in the form of public,truthful announcements. However, little research so far has considered describing andanalysing rational choice between such actions, i.e., predictingwhat rational self-interestedagents actually will or should do. Since the outcome of information exchangeultimately depends on the actions chosen by all the agents in the system, and assumingthat agents have preferences over such outcomes, this is a game theoretic scenario.This is, in our opinion, an interesting general research direction, combining logic andgame theory in the study of rational information exchange. In this article we take somefirst steps in this direction: we consider the case where available actions are publicannouncements, and where each agent has a (typically epistemic) goal formula thatshe would like to become true. What will each agent announce? The truth of the goalformula also depends on the announcements made by other agents. We analyse suchpublic announcement games.publishedVersio

Secure Communication in Disaster Scenarios

Während Naturkatastrophen oder terroristischer Anschläge ist die bestehende Kommunikationsinfrastruktur häufig überlastet oder fällt komplett aus. In diesen Situationen können mobile Geräte mithilfe von drahtloser ad-hoc- und unterbrechungstoleranter Vernetzung miteinander verbunden werden, um ein Notfall-Kommunikationssystem für Zivilisten und Rettungsdienste einzurichten. Falls verfügbar, kann eine Verbindung zu Cloud-Diensten im Internet eine wertvolle Hilfe im Krisen- und Katastrophenmanagement sein. Solche Kommunikationssysteme bergen jedoch ernsthafte Sicherheitsrisiken, da Angreifer versuchen könnten, vertrauliche Daten zu stehlen, gefälschte Benachrichtigungen von Notfalldiensten einzuspeisen oder Denial-of-Service (DoS) Angriffe durchzuführen. Diese Dissertation schlägt neue Ansätze zur Kommunikation in Notfallnetzen von mobilen Geräten vor, die von der Kommunikation zwischen Mobilfunkgeräten bis zu Cloud-Diensten auf Servern im Internet reichen. Durch die Nutzung dieser Ansätze werden die Sicherheit der Geräte-zu-Geräte-Kommunikation, die Sicherheit von Notfall-Apps auf mobilen Geräten und die Sicherheit von Server-Systemen für Cloud-Dienste verbessert

The Expressivity of Quantified Group Announcements

Group announcement logic (GAL) and coalition announcement logic (CAL) allow us to reason about whether it is possible for groups and coalitions of agents to achieve their desired epistemic goals through truthful public communication. The difference between groups and coalitions in such a context is that the latter make their announcements in the presence of possible adversarial counter-announcements. As epistemic goals may involve some agents remaining ignorant, counter-announcements may preclude coalitions from reaching their goals. We study the relative expressivity of GAL and CAL and provide some results involving their more well-known sibling APAL. We also discuss how the presence of memory alters the relationship between groups and coalition

Recent Cases

Recent Case