Refinement laws for verifying library subroutine adaptation

In component-based software engineering programs are constructed from pre-defined software library modules. However, if the library's subroutines do not exactly match the programmer's requirements, the subroutines' code must be adapted accordingly. For this process to be acceptable in safety or mission-critical applications, where all code must be proven correct, it must be possible to verify the correctness of the adaptations themselves. In this paper we show how refinement theory can be used to model typical adaptation steps and to define the conditions that must be proven to verify that a library subroutine has been adapted correctly.

Common and endangered species: How does society allocate support for their conservation?

Examines how society allocates support for species’ conservation when numbers involved are large and resources are limited. Rational behaviour suggests that species in urgent need of conservation will receive more support than those species that are common. However, we demonstrate that in the absence of balanced knowledge common species will receive support more than they would otherwise receive despite society placing high existence values on all species. Twenty four species, both common and endangered and some with a restricted distribution, are examined. We demonstrate that balanced information is vital in order to direct more support for species that are endangered than those that are not. Implications for conservation stemming from the findings are discussed.

A study of the evolution of the representational capabilities of process modeling grammars

A plethora of process modeling techniques has been proposed over the years. One way of evaluating and comparing the scope and completeness of techniques is by way of representational analysis. The purpose of this paper is to examine how process modeling techniques have developed over the last four decades. The basis of the comparison is the Bunge-Wand-Weber representation model, a benchmark used for the analysis of grammars that purport to model the real world and the interactions within it. This paper presents a comparison of representational analyses of several popular process modeling techniques and has two main outcomes. First, it provides insights, within the boundaries of a representational analysis, into the extent to which process modeling techniques have developed over time. Second, the findings also indicate areas in which the underlying theory seems to be over-engineered or lacking in specialization.

Compositional class refinement in object-Z

Object-Z allows coupling constraints between classes which, on the one hand, facilitate specification at a high level of abstraction, but, on the other hand, make class refinement non-compositional. The consequence of this is that refinement is not practical for large Systems. This paper overcomes this limitation by introducing a methodology for compositional class refinement in Object-Z. The key step is an equivalence transformation of an arbitrary Object-Z specification to one in which introduced constraints prohibit non-compositional refinements. The methodology also allows the constraints which couple classes to be refined yielding an unrestricted approach to compositional class refinement.

Context-enhanced authentication for infrastructureless network environments

Infrastructureless networks are becoming more popular with the increased prevalence of wireless networking technology. A significant challenge faced by these infrastructureless networks is that of providing security. In this paper we examine the issue of authentication, a fundamental component of most security approaches, and show how it can be performed despite an absence of trusted infrastructure and limited or no existing trust relationship between network nodes. Our approach enables nodes to authenticate using a combination of contextual information, harvested from the environment, and traditional authentication factors (such as public key cryptography). Underlying our solution is a generic threshold signature scheme that enables distributed generation of digital certificates.

Multi-threaded Communicating Agents in Qu-Prolog

In this tutorial paper we summarise the key features of the multi-threaded Qu-Prolog language for implementing multi-threaded communicating agent applications. Internal threads of an agent communicate using the shared dynamic database used as a generalisation of Linda tuple store. Threads in different agents, perhaps on different hosts, communicate using either a thread-to-thread store and forward communication system, or by a publish and subscribe mechanism in which messages are routed to their destinations based on content test subscriptions. We illustrate the features using an auction house application. This is fully distributed with multiple auctioneers and bidders which participate in simultaneous auctions. The application makes essential use of the three forms of inter-thread communication of Qu-Prolog. The agent bidding behaviour is specified graphically as a finite state automaton and its implementation is essentially the execution of its state transition function. The paper assumes familiarity with Prolog and the basic concepts of multi-agent systems.

Linking job insecurity to negative decision making: The mediating role of job tension

Job insecurity has increased markedly in the developed economies of the world (Gray, 2002). The effects of job insecurity on individual employees and on organisational outcomes, however, are controversial. For instance, Greenhalgh and Rosenblatt (1984) point out that job insecurity can result in increased work effort, while Dekker and Schaufeli, (1995) argue that insecurity leads to stress and decreased performance. In this paper, we outline a study examining the indirect impact of job insecurity on decision-making, via job-related tension. Based on a web survey involving 217 participants, we found that job insecurity indirectly increased the adoption of negative decision-making strategies by increasing employees’ level of job-related tension. Limitations and implications for theory and managers are also discussed.

Forces from highly focused laser beams: Modeling, measurement and application to refractive index measurements

The optical forces in optical tweezers can be robustly modeled over a broad range of parameters using generalsed Lorenz–Mie theory. We describe the procedure, and show how the combination of experimental measurement of properties of the trap coupled with computational modeling, can allow unknown parameters of the particle—in this case, the refractive index—to be determined.