A Semantic Framework to Debug Parallel Lazy Functional Languages

It is not easy to debug lazy functional programs. The reason is that laziness and higherorder complicates basic debugging strategies. Although there exist several debuggers for sequential lazy languages, dealing with parallel languages is much harder. In this case, it is important to implement debugging platforms for parallel extensions, but it is also important to provide theoretical foundations to simplify the task of understanding the debugging process. In this work, we deal with the debugging process in two parallel languages that extend the lazy language Haskell. In particular, we provide an operational semantics that allows us to reason about our parallel extension of the sequential debugger Hood. In addition, we show how we can use it to analyze the amount of speculative work done by the processes, so that it can be used to optimize their use of resources

A Uniform Approach to Programming the World Wide Web

We propose a uniform model for programming distributed Web applications. The model is based on the concept of Web computation places and provides mechanisms to coordinate distributed computations at these places, including peer-to-peer communication between places and a uniform mechanism to initiate computation in remote places. Computations can interact with the flow of HTTP requests and responses, typically as clients, proxies or servers in the Web architecture. We have implemented the model using the global pointers and remote service requests provided by the Nexus communication library. We present the model and its rationale, with some illustrative examples, and we describe the implementation

Study, evaluation and contributions to new algorithms for the embedding problem in a network virtualization environment

Network virtualization is recognized as an enabling technology for the future Internet. It aims to overcome the resistance of the current Internet to architectural change and to enable a new business model decoupling the network services from the underlying infrastructure. The problem of embedding virtual networks in a substrate network is the main resource allocation challenge in network virtualization and is usually referred to as the Virtual Network Embedding (VNE) problem. VNE deals with the allocation of virtual resources both in nodes and links. Therefore, it can be divided into two sub-problems: Virtual Node Mapping where virtual nodes have to be allocated in physical nodes and Virtual Link Mapping where virtual links connecting these virtual nodes have to be mapped to paths connecting the corresponding nodes in the substrate network. Application of network virtualization relies on algorithms that can instantiate virtualized networks on a substrate infrastructure, optimizing the layout for service-relevant metrics. This class of algorithms is commonly known as VNE algorithms. This thesis proposes a set of contributions to solve the research challenges of the VNE that have not been tackled by the research community. To do that, it performs a deep and comprehensive survey of virtual network embedding. The first research challenge identified is the lack of proposals to solve the virtual link mapping stage of VNE using single path in the physical network. As this problem is NP-hard, existing proposals solve it using well known shortest path algorithms that limit the mapping considering just one constraint. This thesis proposes the use of a mathematical multi-constraint routing framework called paths algebra to solve the virtual link mapping stage. Besides, the thesis introduces a new demand caused by virtual link demands into physical nodes acting as intermediate (hidden) hops in a path of the physical network. Most of the current VNE approaches are centralized. They suffer of scalability issues and provide a single point of failure. In addition, they are not able to embed virtual network requests arriving at the same time in parallel. To solve this challenge, this thesis proposes a distributed, parallel and universal virtual network embedding framework. The proposed framework can be used to run any existing embedding algorithm in a distributed way. Thereby, computational load for embedding multiple virtual networks is spread across the substrate network Energy efficiency is one of the main challenges in future networking environments. Network virtualization can be used to tackle this problem by sharing hardware, instead of requiring dedicated hardware for each instance. Until now, VNE algorithms do not consider energy as a factor for the mapping. This thesis introduces the energy aware VNE where the main objective is to switch off as many network nodes and interfaces as possible by allocating the virtual demands to a consolidated subset of active physical networking equipment. To evaluate and validate the aforementioned VNE proposals, this thesis helped in the development of a software framework called ALgorithms for Embedding VIrtual Networks (ALEVIN). ALEVIN allows to easily implement, evaluate and compare different VNE algorithms according to a set of metrics, which evaluate the algorithms and compute their results on a given scenario for arbitrary parameters

Migration, Integration, Asylum: Political Developments in Germany 2017

Der Politikbericht 2017 der deutschen nationalen Kontaktstelle für das Europäische Migrationsnetzwerk (EMN) bietet einen Überblick über die wichtigsten politischen Diskussionen sowie Entwicklungen des Jahres 2017 in den Bereichen legale Migration, internationaler Schutz und Asyl, unbegleitete Minderjährige, Integration und Antidiskriminierung, irreguläre Migration, Rückkehr, Menschenhandel sowie Migration und Entwicklung. Im Jahr 2017 wurden mehrere strukturelle, rechtliche und diskursive Veränderungen in den Bereichen Asyl und Migration angestoßen. Die Bundestagswahl am 24. September 2017 war neben den vier Landtagswahlen in Nordrhein-Westfalen, Niedersachsen, Saarland und Schleswig-Holstein dafür ausschlaggebend. Sowohl der Wahlkampf als auch die anschließenden Koalitionsverhandlungen und die mediale Berichterstattung waren von migrations- und asylpolitischen Kontroversen geprägt.The 2017 Policy Report of the German National Contact Point for the European Migration Network (EMN) provides an overview of the most important political debates and developments in the year 2017 in the areas legal migration, international protection and asylum, unaccompanied minors and other vulnerable persons, integration and anti discrimination measures, irregular migration, return, human trafficking and migration and development. 2017 saw several structural, legal and discursive changes in the area of migration and asylum. Amongst others, these were triggered by four Land elections (North Rhine Westphalia, Lower Saxony, Saarland and Schleswig Holstein) and in particular the Bundestag elections on 24 September 2017. Migration and aslum policy controversies played a major role during the election campaign and the coalition negotiations and were an important issue in the media as well

Voting behavior and electoral choice using causal inference methods for observational data

Which role do the costs and benefits of voting play for the decision of a voter to participate in an election? Does turnout affect the aggregate choice of the electorate? Are incumbents held to account by voters? How do electoral institutions affect the link between incumbent performance and voting behavior? And how can we address these questions given the complex socio-economic and political environment citizens, politicians and parties interact in? In this thesis, I answer questions on “Voting Behavior and Electoral Choice Using Causal Inference Methods for Observational Data.” I inquire representation, accountability and responsiveness, and the role institutions and information play therein - all central factors for understanding how democracy works. These questions are notoriously challenging to address. Strategic incentives and complex interrelations of all involved actors give rise to serious endogeneity problems. This dissertation therefore draws on a design-based approach, using quasi-experimental evidence to contribute to our understanding on the link between citizens, elected representatives and policy. I employ recent methodical innovations in difference-in-difference estimation, matching strategies or instrumental variables, mostly when analyzing administrative electoral data on the aggregate level, augmented by individual level survey data to study the causal mechanisms involved. My research presented in this cumulative dissertation is partially co-authored with Thomas Däubler, Patrick Kuhn, Arndt Leininger and Steffen Zittlau. A first set of papers is concerned with individual vote choice and aggregate electoral outcomes following information shocks and institutional differences. I show whether and how voters use information to mandate future leaders and hold politicians to account for their performance, and that this link is mediated by institutional features. In particular, I argue that information revealed by sudden shocks such as natural disasters is used in a forward-looking selection logic and not only following a retrospective reward-punishment mechanism. However, the institutional features that affect the linkage between voters and politicians matter a great deal; especially the electoral system affects whether primarily party based or as well candidate centered accountability can occur. We make the argument that voters can more easily hold politicians to account for scandalous behavior when voting in an open list proportional representation systems with a two-dimensional party and candidate choice, as compared to single-member district elections. Finally, I argue that incumbents enjoy an electoral advantage (potentially endangering accountability) and show that this can even spill over to other electoral Arenas. In a second set of research papers, I assess causes and consequences of electoral participation as a precondition for representation and responsive governance. We show that voting costs matter. E.g., weather shocks likely increase the personal costs of voting and hence depress turnout; as these shocks are not only geographically clustered but affect some citizens more than others, this has consequences for aggregate electoral choice and representation. I trace the electoral effects of turnout and argue that changes in costs can have consequences for which parts of the population are mobilized to vote; therefore, moderate increases in turnout need not increase the representativeness of turnout. These consequences are important for evaluating institutional features that affect the cost-benefit calculation of electoral participation. Particularly, we show that electoral timing, in our case concurrently held elections, can strongly influence the benefits of electoral participation and lead to substantial increases in turnout. This again has consequences for which groups in the electorate turn out, hence as well for average voter characteristics and finally representation and policy choice. My work draws on causal inference methods for observational data and highlights the role of research design for estimating internally valid effects. All papers use a difference-in-difference strategy: I make the general argument that selection bias from unobservable confounders can be mitigated by using a difference-in-difference framework and/or employing fixed effects models. Drawing on placebo and balance tests, the differencing strategy can even identify causal effects outright where it is plausible that event-affected observations would have counterfactually followed the same trend as control cases. In three applications, we suggest a difference-in-tiers approach, exploiting the fact that voters vote in two tiers in many German elections, where party factors affect the vote similarly across both tiers, but candidate effects plausibly affect only one of the votes. Where differencing methods are not sufficient to induce as-if-random treatment assignment, I combine them with matching approaches to construct valid control groups. Finally, in one case each I draw on an instrumental variable setting and on (geographical) discontinuities to answer the substantive questions I am interested in. Overall, the papers in this thesis show that the design-based approach to political science questions is a highly useful methodological perspective to isolate substantively intriguing relationships between social variables. The thesis contains an introductory chapter, where I summarize my core findings and link them to the broader literature on electoral systems, vote choice and participation, as well as the credibility revolution in political science. Subsequently, the published version of four, and the working paper version of two of the papers, and the respective paper appendices follow as individual chapters.Welche Rolle spielen die Kosten und Nutzen des Wahlprozesses für die Beteiligungsentscheidung? Hat die Höhe der Wahlbeteiligung elektorale Konsequenzen? Wie werden Repräsentanten ausgewählt, wie werden sie zur Rechenschaft gezogen? Beeinflussen institutionelle Regeln die Beziehung zwischen Performanz und Abstimmungsverhalten? Und wie lassen sich solche Fragen angesichts komplexer sozialer und politischer Interaktionen untersuchen? In dieser Dissertationsschrift widme ich mich Fragen zu „Voting Behavior and Electoral Choice Using Causal Inference Methods for Observational Data.“ Ich untersuche Aspekte von Repräsentation, der Verantwortlichkeit von Mandatsträgern, von Responsivität sowie der Rolle von Institutionen und Informationen hierbei. Diese Themen sind zentral für das Verständnis demokratischer Prozesse. Die Untersuchung dieser Fragen stellt jedoch eine methodische Herausforderung dar: Vielfältige strategische Anreize und komplexe Beziehungen zwischen den beteiligten Akteuren führen zu Endogenitätsproblemen, die zwingend bei der empirischen Analyse beachtet werden müssen. In dieser Dissertation wähle ich daher einen design-basierten Ansatz und nutze quasi-experimentelle Techniken – mit dem Ziel, zu unserem Verständnis der Beziehung zwischen Bürgern, gewählten Repräsentanten und Politikentscheidungen beizutragen. Ich nutze methodische Innovationen in der Weiterentwicklung von Differenzenschätzern, Matching-Ansätzen oder Instrumentalvariablen. Dabei analysiere ich überwiegend administrative elektorale Aggregatdaten. Umfragedaten auf Individualebene kommen zusätzlich zum Einsatz, um kausale Mechanismen tiefergehend zu untersuchen. Meine Forschung in dieser kumulativen Dissertationsschrift ist teilweise in Koautorschaft mit Thomas Däubler, Patrick Kuhn, Arndt Leininger und Steffen Zittlau entstanden. Die ersten drei Aufsätze beschäftigen sich mit der Frage ob bzw. wie Wähler in ihrer Wahlentscheidung Informationen nutzen und auf welche Weise Institutionen Verantwortlichkeit beeinflussen. Insbesondere argumentiere ich, dass Informationen zu Regierungshandeln, hier durch das plötzliche Auftreten einer Hochwasserkatastrophe, nicht nur retrospektiv im Sinne einer Belohnungs-Bestrafungs-Logik, sondern auch prospektiv zur Selektion und Mandatierung einer „guten“ Regierung genutzt wird. Institutionelle Faktoren mediieren, inwiefern solche Faktoren auf die Wahlentscheidung Einfluss haben können: Besonders das Wahlsystem bestimmt mit darüber, ob Rechenschaft gegenüber dem Wähler primär parteizentriert oder auch kandidatenzentriert stattfindet. Wir vergleichen dazu Prozesse der Verantwortlichkeit in einem offenen Listenwahlsystem und einem System relativer Mehrheitswahl in Einerwahlkreisen: Nach einem öffentlichen Skandal erlaubt Ersteres dem Wähler nicht nur eine Entkopplung von Partei- und Kandidatenentscheidung, sondern ist zudem responsiver bezüglich kleiner Änderungen in Stimmenanteilen. Die Institution eines offenen Listenwahlsystems befördert daher kandidatenzentrierte Verantwortlichkeit. Dies gilt jedoch nur ceteris paribus. Amtsinhaber besitzen etwa einen elektoralen Bonus: Ich zeige, dass dieser sogar in andere elektorale Arenen überspringen kann. Die zweiten drei Aufsätze behandeln Ursachen und Konsequenzen von Wahlbeteiligung als grundlegendem Faktor für gute Repräsentation und responsive Politik. Wir weisen nach, dass die Kosten der Wahl eine Rolle spielen. Wetterereignisse beeinflussen diese etwa, was zu einem Rückgang der Wahlbeteiligung führt. Da ein derartiger Rückgang zum einen geographisch geclustert ist, zum anderen manche Bürger stärker auf Veränderungen hinsichtlich der Kosten reagieren, hat dies Konsequenzen für die Wahl des Elektorats und Repräsentation. Ich argumentiere hier insbesondere, dass auch eine Erhöhung der Wahlbeteiligung elektorale Effekte haben kann, die nicht zwangsläufig auf höherer Repräsentativität beruhen. Für die Bewertung der Auswirkungen institutioneller Regelungen, die die Nutzen und Kosten der Wahl beeinflussen, ist dies ein wichtiger Aspekt. Wir zeigen etwa, dass der Wahlzyklus, hier die Gleichzeitigkeit mehrerer Abstimmungen, einen starken Einfluss auf die aggregierte Wahlbeteiligung haben kann. Dies impliziert, dass sich manche gesellschaftlichen Gruppen relativ mehr, andere relativ weniger beteiligen. Dadurch unterscheidet sich der Medianwähler, was wiederum vermutlich Implikationen für Policy-Entscheidungen der Regierung hat. Diese Anwendungen greifen alle auf Methoden der kausalen Inferenz mit Beobachtungsdaten zurück und betonen die Rolle des Forschungsdesigns für intern valide Ergebnisse. Insbesondere nutze ich Differenzenschätzer als Methode, die generell geeignet ist, Selektionsverzerrung durch unbeobachtete, zeitinvariante Störfaktoren zu reduzieren. Der Ansatz erlaubt gar direkt kausale Schlussfolgerungen, wenn Placebo- oder Balance-Tests es plausibel erscheinen lassen, dass Beobachtungen der Kontrollgruppe tatsächlich den kontrafaktischen Trend der Treatmentgruppe (d.h. den Trend ohne das Treatment) abbilden. In drei Anwendungsfällen zeige ich die Eignung von Differenzenschätzern über die temporale Dimension hinaus, etwa indem wir diese auf aggregierte Unterschiede in Abstimmungsmodi (Erst- und Zweitstimme) beziehen, um gemeinsam zugrundeliegende Parteifaktoren implizit zu kontrollieren und Kandidatenfaktoren in der Wahlentscheidung zu isolieren. Wo die zentrale Annahme an Differenzenschätzer, parallele Trends, möglicherweise verletzt ist, kombiniere ich sie etwa mit Matching-Ansätzen, um valide Kontrollgruppen zu konstruieren. Einzelne Anwendungen nutzen zudem Instrumentalvariablenschätzer oder geographische Diskontinuitäten, um Effekte zu identifizieren. Insgesamt zeigen diese Anwendungen, dass eine design-basierte methodische Herangehensweise an sozialwissenschaftliche Fragestellungen sehr gewinnbringend ist und es gelingen kann, die substanziell interessierenden Variablenbeziehungen auch mit Beobachtungsdaten quasi-experimentell zu isolieren. Diese Dissertation besteht aus einem Einleitungskapitel, in dem ich meine zentralen Ergebnisse zusammenfasse und sie mit der Wahlsystem-, Wahlentscheidungs-, und Partizipationsliteratur sowie mit der methodologischen Literatur zu kausaler Inferenz (mit Beobachtungsdaten) verknüpfe. Daran schließen sich in sechs Kapiteln die veröffentlichte Version von vier, sowie die Manuskript-Version von zwei Aufsätzen an. Zuletzt folgen in weiteren Kapiteln die jeweiligen Appendizes

Making EU foreign policy towards a 'Pariah' state: consensus on sanctions in EU foreign policy towards Myanmar

This thesis seeks to explain why the European Union ratcheted up restrictive measures on Myanmar from 1991 until 2010, despite divergent interests of EU member states and the apparent inability of sanctions to quickly achieve the primary objectives of EU policy. This empirical puzzle applies the ‘sanctions paradox’ to the issue of joint action in the EU. It also connects the assessment of policy effectiveness to EU foreign policy-making. The investigation unravels this conundrum through competitive theory testing. The study discovers that EU foreign policy was essentially decided by the largest member states. Since 1996, the UK has fostered a consensus among EU policymakers on a principled common policy, which would induce political reform in Myanmar mainly via the implementation of punitive measures. Hence, noncompliance by the target with EU demands offers a credible, but insufficient explanation of why the EU tightened its sanctions regime. US pressure on EU policy was marginal. The dissertation argues that a ‘normative’ interpretation of liberal intergovernmentalism best solves this puzzle. The EU met domestic pressures for action, although the measures adopted were clearly too inadequate to be effective. Feedback on policy effectiveness did not play a significant role in EU decision-making. EU policy was driven by a consensus to treat Myanmar as a ‘pariah’ state. Ideological motivations have largely outweighed material interests. Normative arguments were necessary to put proposals on the common agenda; yet, decisions ultimately involved ‘cooperative bargaining’ among the largest states. Consensus building was therefore a dynamic process. The policy entrepreneur defined its interests domestically; member states with lower preference intensity generally refrained from opposing its leadership. This thesis thus contributes to the liberal intergovernmental scholarship by proposing a more comprehensive explanation for the drivers and constraints that influence the making of European sanctions