Safety-Aware Apprenticeship Learning

Apprenticeship learning (AL) is a kind of Learning from Demonstration techniques where the reward function of a Markov Decision Process (MDP) is unknown to the learning agent and the agent has to derive a good policy by observing an expert's demonstrations. In this paper, we study the problem of how to make AL algorithms inherently safe while still meeting its learning objective. We consider a setting where the unknown reward function is assumed to be a linear combination of a set of state features, and the safety property is specified in Probabilistic Computation Tree Logic (PCTL). By embedding probabilistic model checking inside AL, we propose a novel counterexample-guided approach that can ensure safety while retaining performance of the learnt policy. We demonstrate the effectiveness of our approach on several challenging AL scenarios where safety is essential.Comment: Accepted by International Conference on Computer Aided Verification (CAV) 201

Probabilistic Timed Automata with Clock-Dependent Probabilities

Probabilistic timed automata are classical timed automata extended with discrete probability distributions over edges. We introduce clock-dependent probabilistic timed automata, a variant of probabilistic timed automata in which transition probabilities can depend linearly on clock values. Clock-dependent probabilistic timed automata allow the modelling of a continuous relationship between time passage and the likelihood of system events. We show that the problem of deciding whether the maximum probability of reaching a certain location is above a threshold is undecidable for clock-dependent probabilistic timed automata. On the other hand, we show that the maximum and minimum probability of reaching a certain location in clock-dependent probabilistic timed automata can be approximated using a region-graph-based approach.Comment: Full version of a paper published at RP 201

Science for Global Ubiquitous Computing

This paper describes an initiative to provide theories that can underlie the development of the Global Ubiquitous Computer, the network of ubiquitous computing devices that will pervade the civilised world in the course of the next few decades. We define the goals of the initiative and the criteria for judging whether they are achieved; we then propose a strategy for the exercise. It must combine a bottom-up development of theories in directions that are currently pursued with success, together with a top-down approach in the form of collaborative projects relating these theories to engineered systems that exist or are imminent

Multicultural identity integration versus compartmentalization as predictors of subjective well-being for Third Culture Kids: The mediational role of self-concept consistency and self-efficacy

Globalization has resulted in an exponential increase in the number of Third Culture Kids (TCKs), defined as being raised in a culture other than that of their parents (or the passport country) and meaningfully interacting with different cultures. Inconsistencies regarding the effect of multicultural and transient experiences on well-being exist in the psychological literature. We aimed to reveal associations between multicultural identity configurations (integration, categorization, compartmentalization) and well-being with the mediating role of self-concept consistency and self-efficacy. Participants ( = 399, = 21.2 years) were students at an international university in the United Arab Emirates. We used the Multicultural Identity Integration Scale, the Berne Questionnaire of Subjective Well-Being, the General Self-Efficacy Scale, and the Self-Consistency Subscale from the Self-Construal Scale. The findings suggest that not merely exposure to diversity but also internal integration versus identity compartmentalization moderate the well-being of TCKs. We explained such mechanisms via partial mediation of self-consistency and self-efficacy. Our study contributed to a better understanding of the TCKs' identity paradigm and pointed to multicultural identity integration as vital to TCKs' well-being via its effect on self-consistency and self-efficacy. Conversely, identity compartmentalization decreased well-being via a reduction in the sense of self-consistency

PRISM: a tool for automatic verification of probabilistic systems

Probabilistic model checking is an automatic formal verification technique for analysing quantitative properties of systems which exhibit stochastic behaviour. PRISM is a probabilistic model checking tool which has already been successfully deployed in a wide range of application domains, from real-time communication protocols to biological signalling pathways. The tool has recently undergone a significant amount of development. Major additions include facilities to manually explore models, Monte-Carlo discrete-event simulation techniques for approximate model analysis (including support for distributed simulation) and the ability to compute cost- and reward-based measures, e.g. "the expected energy consumption of the system before the first failure occurs". This paper presents an overview of all the main features of PRISM. More information can be found on the website: www.cs.bham.ac.uk/~dxp/prism

Evaluating the reliability of NAND multiplexing with PRISM

Probabilistic-model checking is a formal verification technique for analyzing the reliability and performance of systems exhibiting stochastic behavior. In this paper, we demonstrate the applicability of this approach and, in particular, the probabilistic-model-checking tool PRISM to the evaluation of reliability and redundancy of defect-tolerant systems in the field of computer-aided design. We illustrate the technique with an example due to von Neumann, namely NAND multiplexing. We show how, having constructed a model of a defect-tolerant system incorporating probabilistic assumptions about its defects, it is straightforward to compute a range of reliability measures and investigate how they are affected by slight variations in the behavior of the system. This allows a designer to evaluate, for example, the tradeoff between redundancy and reliability in the design. We also highlight errors in analytically computed reliability bounds, recently published for the same case study

New Ecological Paradigm and third culture kids: Multicultural identity configurations, global mindset and values as predictors of environmental worldviews

Ecological degradation threatens human survival, increasing the need to understand factors related to pro‐environmental attitudes and worldviews. In a globalising world, new paradigms arise as central to social sciences, including the New Ecological Paradigm (NEP) and the multicultural identities of individuals raised between the cultures, third culture kids (TCKs). NEP is an ecocentric perspective that stresses the interdependence between nature and humans, opposite to anthropocentrism. TCKs' exposure to cultural diversity during developmental years might support global issues engagement and ecocentric worldviews. The present study focused on non‐Western TCKs (N = 399; mean age 21 years), aiming to explore whether multicultural identity configurations (integration, categorisation, compartmentalisation), values dimensions (self‐transcendence, openness and conservation) and global mindset predicted ecocentric and anthropocentric worldviews. The results demonstrated that TCKs were ecocentrically inclined. The path model revealed that ecocentrism could be directly positively predicted by integrated multicultural identity, self‐transcendence and a global mindset. Anthropocentrism was predicted by multicultural identity categorisation and conservation values. Also, values of self‐transcendence and openness buffered the impact of compartmentalisation and categorisation on ecocentrism and anthropocentrism. This study set innovative directions in multiculturism and environmentalism discourse through understanding a multicultural identity's relationships with pro‐environmental attitudes

Assume-guarantee verification for probabilistic systems

We present a compositional verification technique for systems that exhibit both probabilistic and nondeterministic behaviour. We adopt an assume- guarantee approach to verification, where both the assumptions made about system components and the guarantees that they provide are regular safety properties, represented by finite automata. Unlike previous proposals for assume-guarantee reasoning about probabilistic systems, our approach does not require that components interact in a fully synchronous fashion. In addition, the compositional verification method is efficient and fully automated, based on a reduction to the problem of multi-objective probabilistic model checking. We present asymmetric and circular assume-guarantee rules, and show how they can be adapted to form quantitative queries, yielding lower and upper bounds on the actual probabilities that a property is satisfied. Our techniques have been implemented and applied to several large case studies, including instances where conventional probabilistic verification is infeasible

Explicit Model Checking of Very Large MDP using Partitioning and Secondary Storage

The applicability of model checking is hindered by the state space explosion problem in combination with limited amounts of main memory. To extend its reach, the large available capacities of secondary storage such as hard disks can be exploited. Due to the specific performance characteristics of secondary storage technologies, specialised algorithms are required. In this paper, we present a technique to use secondary storage for probabilistic model checking of Markov decision processes. It combines state space exploration based on partitioning with a block-iterative variant of value iteration over the same partitions for the analysis of probabilistic reachability and expected-reward properties. A sparse matrix-like representation is used to store partitions on secondary storage in a compact format. All file accesses are sequential, and compression can be used without affecting runtime. The technique has been implemented within the Modest Toolset. We evaluate its performance on several benchmark models of up to 3.5 billion states. In the analysis of time-bounded properties on real-time models, our method neutralises the state space explosion induced by the time bound in its entirety.Comment: The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-319-24953-7_1