Behavioural Types for Actor Systems

Recent mainstream programming languages such as Erlang or Scala have renewed the interest on the Actor model of concurrency. However, the literature on the static analysis of actor systems is still lacking of mature formal methods. In this paper we present a minimal actor calculus that takes as primitive the basic constructs of Scala's Actors API. More precisely, actors can send asynchronous messages, process received messages according to a pattern matching mechanism, and dynamically create new actors, whose scope can be extruded by passing actor names as message parameters. Drawing inspiration from the linear types and session type theories developed for process calculi, we put forward a behavioural type system that addresses the key issues of an actor calculus. We then study a safety property dealing with the determinism of finite actor com- munication. More precisely, we show that well typed and balanced actor systems are (i) deadlock-free and (ii) any message will eventually be handled by the target actor, and dually no actor will indefinitely wait for an expected messag

Judging Risk

Risk assessment plays an increasingly pervasive role in criminal justice in the United States at all stages of the process, from policing, to pre-trial, sentencing, corrections, and during parole. As efforts to reduce incarceration have led to adoption of risk-assessment tools, critics have begun to ask whether various instruments in use are valid and whether they might reinforce rather than reduce bias in criminal justice outcomes. Such work has neglected how decisionmakers use risk-assessment in practice. In this Article, we examine in detail the judging of risk assessment and we study why decisionmakers so often fail to consistently use such quantitative information

Syrian Refugees and the Digital Passage to Europe: Smartphone Infrastructures and Affordances

This research examines the role of smartphones in refugees’ journeys. It traces the risks and possibilities afforded by smartphones for facilitating information, communication, and migration flows in the digital passage to Europe. For the Syrian and Iraqi refugee respondents in this France-based qualitative study, smartphones are lifelines, as important as water and food. They afford the planning, navigation, and documentation of journeys, enabling regular contact with family, friends, smugglers, and those who help them. However, refugees are simultaneously exposed to new forms of exploitation and surveillance with smartphones as migrations are financialised by smugglers and criminalized by European policies, and the digital passage is dependent on a contingent range of sociotechnical and material assemblages. Through an infrastructural lens, we capture the dialectical dynamics of opportunity and vulnerability, and the forms of resilience and solidarity, that arise as forced migration and digital connectivity coincide

Buying commercial law: Choice of law, choice of forum, and network externalities

Copyright @ 2009 Bryan DruzinThis paper applies network effect theory to transnational commercial law, arguing that commercial parties selecting law through choice of law and choice of forum clauses can be likened to consumers selecting a product, and thus equally susceptible to the effects of network externalities. The number of “consumers” who subscribe to the same legal norms is analogous to the number of consumers who use a product. As the number of “consumers” increases, so too does the inherent value of selecting that jurisdiction, inducing even more parties to “purchase” that body of law. This is a network effect. I argue that transnational commercial law is ideally calibrated so as to generate a network effect. This stems from the inherent nature of commerce. The discussion distinguishes between two kinds of externalities, direct and indirect network externalities, concluding that network systems that possess both kinds of network externalities (as is the case with law-selection decisions in commercial contracts), are the best candidates to produce a robust network effect. I then examine how the twin ingredients of fluid interaction and frequent choice present in commerce precipitate a network effect; expansive interaction places a higher premium on the need for synchronization, and frequent opportunities to select law in the contracts of fresh commercial relationships allow for an incremental drift towards a specific jurisdiction. The paper ultimately concludes that, as a result, network externalities indeed play an influential role in the ascension of particular jurisdictions over others in law-selection decisions, an important conclusion as it points to an unrecognized influence underpinning the current development of transnational commercial law

Modular session types for objects

Session types allow communication protocols to be specified type-theoretically so that protocol implementations can be verified by static type checking. We extend previous work on session types for distributed object-oriented languages in three ways. (1) We attach a session type to a class definition, to specify the possible sequences of method calls. (2) We allow a session type (protocol) implementation to be modularized, i.e. partitioned into separately-callable methods. (3) We treat session-typed communication channels as objects, integrating their session types with the session types of classes. The result is an elegant unification of communication channels and their session types, distributed object-oriented programming, and a form of typestate supporting non-uniform objects, i.e. objects that dynamically change the set of available methods. We define syntax, operational se-mantics, a sound type system, and a sound and complete type checking algorithm for a small distributed class-based object-oriented language with structural subtyping. Static typing guarantees that both sequences of messages on channels, and sequences of method calls on objects, conform to type-theoretic specifications, thus ensuring type-safety. The language includes expected features of session types, such as delegation, and expected features of object-oriented programming, such as encapsulation of local state.Comment: Logical Methods in Computer Science (LMCS), International Federation for Computational Logic, 201

Size Matters: Microservices Research and Applications

In this chapter we offer an overview of microservices providing the introductory information that a reader should know before continuing reading this book. We introduce the idea of microservices and we discuss some of the current research challenges and real-life software applications where the microservice paradigm play a key role. We have identified a set of areas where both researcher and developer can propose new ideas and technical solutions.Comment: arXiv admin note: text overlap with arXiv:1706.0735