A Classification of Models for Concurrency

Models for concurrency can be classified with respect to the three relevant parameters: behaviour/system, interleaving/noninterleaving, linear/branching time. When modelling a process, a choice concerning such parameters corresponds to choosing the level of abstraction of the resulting semantics. The classifications are formalised through the medium of category theory

Deterministic Behavioural Models for Concurrency

This paper offers three candidates for a deterministic, noninterleaving, behaviour model which generalizes Hoare traces to the noninterleaving situation. The three models are all proved equivalent in the rather strong sense of being equivalent as categories. The models are: deterministic labelled event structures, generalized trace languages in which the independence relation is context-dependent, and deterministic languages of pomsets

Relationships between Models for Concurrency

Models for concurrency can be classified with respect to three relevant parameters: behaviour/system, interleaving/noninterleaving, linear/branching time. When modelling a process, a choice concerning such parameters corresponds to choosing the level of abstraction of the resulting semantics. The classifications are formalized through the medium of category theory

Events in computation

SIGLEAvailable from British Library Document Supply Centre- DSC:D36018/81 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Symmetry in concurrent games

Abstract—Behavioural symmetry is introduced into concurrent games. It expresses when plays are essentially the same. A characterization of strategies on games with symmetry is provided. This leads to a bicategory of strategies on games with symmetry. Symmetry helps allay the perhaps overly-concrete nature of games and strategies, and shares many mathematical features with homotopy. In the presence of symmetry we can consider monads for which the monad laws do not hold on the nose but do hold up to symmetry. This broadening of the concept of monad has a dramatic effect on the types concurrent games can support and allows us, for example, to recover the replication needed to express and extend traditional game semantics of programming languages. I

The parallel intensionally fully abstract games model of PCF

International audienceWe describe a framework for truly concurrent game semantics of programming languages, based on Rideau and Winskel's concurrent games on event structures. The model supports a notion of innocent strategy that permits concurrent and non-deterministic behaviour, but which coincides with traditional Hyland-Ong innocent strategies if one restricts to the deterministic sequential case. In this framework we give an alternative interpretation of Plotkin's PCF, that takes advantage of the concurrent nature of strategies and formalizes the idea that although PCF is a sequential language, certain sub-computations are independent and can be computed in a parallel fashion. We show that just as Hyland and Ong's sequential interpretation of PCF, our parallel interpretation yields a model that is intensionally fully abstract for PCF

A programming logic for Java bytecode programs

One significant disadvantage of interpreted bytecode languages, such as Java, is their low execution speed in comparison to compiled languages like C. The mobile nature of bytecode adds to the problem, as many checks are necessary to ensure that downloaded code from untrusted sources is rendered as safe as possible. But there do exist ways of speeding up such systems. One approach is to carry out static type checking at load time, as in the case of the Java Bytecode Verifier. This reduces the number of runtime checks that must be done and also allows certain instructions to be replaced by faster versions. Another approach is the use of a Just In Time (JIT) Compiler, which takes the bytecode and produces corresponding native code at runtime. Some JIT compilers also carry out some code optimization. There are, however, limits to the amount of optimization that can safely be done by the Verifier and JITs; some operations simply cannot be carried out safely without a certain amount of runtime checking. But what if it were possible to prove that the conditions the runtime checks guard against would never arise in a particular piece of code? In this case it might well be possible to dispense with these checks altogether, allowing optimizations not feasible at present. In addition to this, because of time constraints, current JIT compilers tend to produce acceptable code as quickly as possible, rather than producing the best code possible. By removing the burden of analysis from them it may be possible to change this. We demonstrate that it is possible to define a programming logic for bytecode programs that allows the proof of bytecode programs containing loops. The instructions available to use in the programs are currently limited, but the basis is in place to extend these. The development of this logic is non-trivial and addresses several difficult problems engendered by the unstructured nature of bytecode programs

A Comparison of Petri Net Semantics under the Collective Token Philosophy

In recent years, several semantics for place/transition Petri nets have been proposed that adopt the collective token philosophy. We investigate distinctions and similarities between three such models, namely configuration structures, concurrent transition systems, and (strictly) symmetric (strict) monoidal categories. We use the notion of adjunction to express each connection. We also present a purely logical description of the collective token interpretation of net behaviours in terms of theories and theory morphisms in partial membership equational logic

Sex differences in eyewitness memory: A scoping review

Researchers in cognitive and forensic psychology have long been interested in the impact of individual differences on eyewitness memory. The sex of the eyewitness is one such factor, with a body of research spanning over 50 years that has sought to determine if and how eyewitness memory differs between males and females. This research has significant implications across the criminal justice system, particularly in the context of gendered issues such as sexual assault. However, the findings have been inconsistent, and there is still a lack of consensus across the literature. A scoping review and analysis of the literature was performed to examine the available evidence regarding whether sex differences in eyewitness memory exist, what explanations have been proposed for any differences found, and how this research has been conducted. Through a strategic search of seven databases, 22 relevant articles were found and reviewed. Results demonstrated that despite the mixed nature of the methodologies and findings, the research suggests that neither males nor females have superior performance in the total amount of accurate information reported, but rather that females may have better memory for person-related details while males may perform better for details related to the surrounding environment. There was also consistent evidence for the own-gender bias. There was some consensus that differences in selective attention between males and females may underlie these sex differences in eyewitness memory. However, none of the studies directly tested this suggested attentional factor, and thus future research is needed to investigate this using a more systematic and empirical approach