Abduction in Well-Founded Semantics and Generalized Stable Models

Abductive logic programming offers a formalism to declaratively express and solve problems in areas such as diagnosis, planning, belief revision and hypothetical reasoning. Tabled logic programming offers a computational mechanism that provides a level of declarativity superior to that of Prolog, and which has supported successful applications in fields such as parsing, program analysis, and model checking. In this paper we show how to use tabled logic programming to evaluate queries to abductive frameworks with integrity constraints when these frameworks contain both default and explicit negation. The result is the ability to compute abduction over well-founded semantics with explicit negation and answer sets. Our approach consists of a transformation and an evaluation method. The transformation adjoins to each objective literal $O$ in a program, an objective literal $not(O)$ along with rules that ensure that $not(O)$ will be true if and only if $O$ is false. We call the resulting program a {\em dual} program. The evaluation method, \wfsmeth, then operates on the dual program. \wfsmeth{} is sound and complete for evaluating queries to abductive frameworks whose entailment method is based on either the well-founded semantics with explicit negation, or on answer sets. Further, \wfsmeth{} is asymptotically as efficient as any known method for either class of problems. In addition, when abduction is not desired, \wfsmeth{} operating on a dual program provides a novel tabling method for evaluating queries to ground extended programs whose complexity and termination properties are similar to those of the best tabling methods for the well-founded semantics. A publicly available meta-interpreter has been developed for \wfsmeth{} using the XSB system.Comment: 48 pages; To appear in Theory and Practice in Logic Programmin

Patterns of non-employment: How labour market institutions shape social inequality in employment performance in Europe

The central research question of this dissertation is how labor market institutions shape social patterns of employment. More specifically, it analyzes how labour market policies and regulation affect the labour market performance of men and women, different age groups, and educational levels. Before conducting three empirical studies, a framework paper elaborates on why a focus on unemployment is not sufficient when interested in the distribution of employment and the disadvantaged positions of women, youth, older workers and those with low education. I argue that periods of inactivity need to be included and thus non-employment as a whole has to be subject of labour market analysis. Furthermore, the framework develops a macro-micro model of institutional impact on individual employment. It contrasts theoretical expectations of liberal economics with approaches that emphasize the importance of current labour market positions for subsequent careers and longitudinal search and matching processes. The three empirical studies proceed in two steps. First, study 1 quantifies the relationship between institutions and the social composition of non-employment in a multi-country analysis. The analysis establishes that institutional arrangements’ impact is heterogeneous. In general, social risk groups are affected more strongly, both negatively, by employment protection, powerful unions, unemployment insurance and labour taxes, and positively, by active labour market polices, centralized wage bargaining and social assistance. Second, taking a life-course perspective, studies 2 and 3 explore transitions and trajectories out of non-employment in the United Kingdom and Germany. The more strongly regulated German labour market leads to slower transitions back into work and – surprisingly – less stable long-term re-entry compared to the United Kingdom. German transitions and subsequent trajectories also exhibit an increased social inequality. Results from the three studies underline that institutional arrangements, which provide insiders with advantages, increase social inequality, lower overall employment and chances to return to work. Institutional arrangements that regulate the labour market in an indiscriminate way are associated with better social inclusion and higher employment

When The High-Income Country Context Dissolves. Social Policy Preferences in Low- and Middle-Income Democracies

The provision of welfare services can be understood as an iterated public goods game in simplified terms. Individuals contribute via taxation while the state cooperates by the provision of welfare services as return for paid contributions. Focusing on welfare provision in low- and middle-income democracies, where we find decisive variation in state capacity and considerable inefficiencies such as high rates of income inequality, corruption, and a prosperous informal economy, the efficiency of the public goods game becomes uncertain. If the state is perceived as weak and untrustworthy because of lacking capacity to extract revenue and to deliver social services, why should individuals turn towards this low-capacity entity for provision of welfare services? Drawing upon the current debate on redistributive preferences in the political economy literature, the overall research question that this dissertation is concerned with therefore asks: what happens to individual social policy preferences when the context of high-income states dissolves? The dissertation analyses social policy preference formation in the context of increased uncertainty that is reflected by weaknesses in the distributive and extractive capacities of the state and inefficiency – that is, the informal economy. Based on cross-country survey data for a large set of less developed democracies, the study illustrates with the use of hierarchical modeling techniques how context characteristics influence individual preferences, next to micro level factors such as income, education, and labor market status. The analyses reveal a considerable impact of these key features of the public goods game for social policy preferences in low- and middle-income democracies. The dissertation builds a micro-foundation for social policy in low- and middle-income democracies that takes into account the institutional and structural framework of the state and the particularities of a stratified labor market