Distributing the Workload in a Lazy Theorem-Prover

Well-Definedness is important for many formal methods. In B and Event-B it ensures that certain kinds of errors (e.g., division by 0) cannot appear and that proof rules based on two-valued logic are sound. For validation tools such as ProB, well-definedness is important for constraint solving. B and Event-B establish well-definedness by generating dedicated proof obligations (POs). Unfortunately, the standard provers are not always very good at discharging them. In this paper, we present a new integrated technique to simultaneously generate and discharge well-definedness POs. The implementation contains a dedicated rule-based prover written in Prolog supporting B, Event-B and extensions thereof for data validation. We show that the generation and discharging is significantly faster than existing implementations in rodin and Atelier-B and that a large number of POs are automatically discharged. The POs are fine-grained enough to provide precise source code feedback, and allow inspection of problematic POs within various editors.

Using induction and rewriting to verify and complete parameterized specifications

Event-B is a formal modelling method which is claimed to be suitable for diverse modelling domains, such as reactive systems and sequential program development. This claim hinges on the fact that any particular model has an appropriate semantics. In Event-B this semantics is provided implicitly by proof obligations associated with a model. There is no fixed semantics though. In this article we argue that this approach is beneficial to modelling because we can use similar proof obligations across a variety of modelling domains. By way of two examples we show how similar proof obligations are linked to different semantics. A small set of proof obligations is thus suitable for a whole range of modelling problems in diverse modelling domains.KeywordsAbstract EventSequential ProgramProof ObligationAbstract MachineConcrete EventThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Computer networks have become so ubiquitous that the user can access various services by using network devices at anytime and anywhere. However, due to the open nature of the network, the security issue has become an important consideration in these network-based systems that cannot be ignored, especially in critical systems, such as life-critical system and financial system. User authentication scheme is the most used and effective mechanism for information security, and many user authentication schemes have been proposed by researchers. Recently, Shen et al. proposed a biometrics-based user authentication scheme for multi-server environments in critical systems. However, their scheme lacks the wrong password detection mechanism and is vulnerable to denial-of-service attack. Besides, they do not consider the user anonymity property, and may suffer from biometrics template lost attack because the biometrics template is directly stored in user’s smart card. In this paper, an enhanced biometrics-based user authentication scheme for multi-server environments in critical systems is presented by adopting the fuzzy extractor. The analysis shows that the proposed scheme not only removes the security weaknesses of previous schemes, but also keeps the computational efficiency.

Combining decision procedures by (model-)equality propagation

Issues in developing software for safety critical systems

Early data networks were based on point-to-point or multipoint topologies. They were often of a star structure with a central processing unit (CPU) at the star's hub. Terminals in this network were “dumb” terminals and relied on the CPU's processing power for nearly all network activity. When the personal computer (PC) gained wide acceptance, distributed processing became the rule. As a result, data networks and data networking became much more complex. We now see complex multiple star, mesh, and tree like networks where many of the nodes have multiple inlets and outlets. Data rates were based on the limitations of the analog network. In the period of the 2nd edition of this book, this roughly equated to 9600 bps. Today, it is common to have 56-kbps access lines to a larger network where the basic channel data rate is 64 kbps. We can bring together these basic building blocks of 64 kbps to form aggregate channels of 128, 256, and 384 kbps up to 1.536 Mbps or 1.984 Mbps. Data protocols instilled order out of contentious chaos in data network operation. These protocols, applying to wide area networks (WANs), are the principal thrust of the chapter. Most are based on shipping user data in packets or frames. We discuss the transport of user data in cells in Chapter 28. Most packet networks are based on CCITT Rec. X.25. If we widen the definition of packet networks to include the transmission control protocol/internet protocol (TCP/IP), certainly X.25 will have a competitor. Both TCP/IP and X.25 have a comparatively high latency (latency is the time it takes from initiation to completion of a data transaction). Frame relay was introduced in the same period. This is a comparatively low latency system. This section provides design data and brief descriptions of wide area data networking as a whole with hypothetical reference circuits, the archetypical data link layer protocol, high-level data link control (HDLC), X.25 and its companion, link access protocol B-layer (LAPB), TCP/IP family of protocols, frame relay family of protocols, and a brief description of SMDS (switched multimegabit data service). Variants of LAPD are discussed in the frame relay section of this chapter. Keywords: enterprise networks; universal application; high-level data-link control; packet-switched; virtual connections; transmission control protocol; internet protocol; ISO transport protocol; frame relay; switched multimegabit data service; internetworking; ITU-T rec X.75; data network management

Nowadays developing methods for distributed computing is received much attention. One of the methods of distributed computing is using of multi-agent systems. The organization of distributed computing based on the conventional network computers can experience security threats performed by computational processes. Authors have developed the unified agent algorithm of control system of computing network nodes operation. Network PCs is used as computing nodes. The proposed multi-agent control system for the implementation of distributed computing allows in a short time to organize using of the processing power of computers any existing network to solve large-task by creating a distributed computing. Agents based on a computer network can: configure a distributed computing system; to distribute the computational load among computers operated agents; perform optimization distributed computing system according to the computing power of computers on the network. The number of computers connected to the network can be increased by connecting computers to the new computer system, which leads to an increase in overall processing power. Adding multi-agent system in the central agent increases the security of distributed computing. This organization of the distributed computing system reduces the problem solving time and increase fault tolerance (vitality) of computing processes in a changing computing environment (dynamic change of the number of computers on the network). Developed a multi-agent system detects cases of falsification of the results of a distributed system, which may lead to wrong decisions. In addition, the system checks and corrects wrong results.

Hybrid coding with pre-buffering and pre-analysis in a software-based codec environment

We demonstrate the characteristics of 2 mm to 1 cm long vertical-cavity surface-emitting laser (VCSEL) amplifiers that emitted continuous wave (CW). VCSELs have various applications in different fields, including datacom, optical interconnects, printers, and sensors. However, VCSEL technology has not been applied in laser material processing that needs a light source with high power density. This is because single-mode (SM) VCSELs have fundamental difficulty in producing beams having an output power of more than several milliwatts. On the contrary, the application range of VCSEL amplifiers is expected to be extended into fields that simultaneously require lasers with high power and high beam quality because they have the potential to attain both characteristics. In this paper, we demonstrate the CW operation of high-power SM 2 mm to 1 cm long VCSEL amplifiers that had an output power of several watts at 20 °C. By optimizing the top-mirror reflectivity and seed-laser wavelength, the output power was linearly proportional to the amplifier length when the growth of amplified spontaneous emission (ASE) was suppressed. The I–L characteristics for different amplifier lengths were measured. All devices emitted narrow beams with divergence angles of approximately 0.1°. The maximum SM output power of the devices with lengths of 2 mm, 6 mm, and 1 cm were 0.62, 2.13, and 3.25 W, respectively. This result shows the possibility to achieve high power and high beam quality for direct semiconductor laser processing.

Early data networks were based on point‐to‐point or multipoint topologies. They were often of a star structure with a central processing unit (CPU) at the star's hub. Terminals in this network were “dumb” terminals and relied on the CPU's processing power for nearly all network activity.When the personal computer (PC) gained wide acceptance, distributed processing became the rule. As a result, data networks and data networking became much more complex. We now see complex multiple star, mesh, and tree like networks where many of the nodes have multiple inlets and outlets.Data rates were based on the limitations of the analog network. In the period of the 2nd edition of this book, this roughly equated to 9600 bps. Today, it is common to have 56‐kbps access lines to a larger network where the basic channel data rate is 64 kbps. We can bring together these basic building blocks of 64 kbps to form aggregate channels of 128, 256, and 384 kbps up to 1.536 Mbps or 1.984 Mbps.Data protocols instilled order out of contentious chaos in data network operation. These protocols, applying to wide area networks (WANs), are the principal thrust of the chapter. Most are based on shipping user data in packets or frames. We discuss the transport of user data in cells in Chapter 28.Most packet networks are based on CCITT Rec.X.25. If we widen the definition of packet networks to include the transmission control protocol/internet protocol (TCP/IP), certainly X.25 will have a competitor. Both TCP/IP and X.25 have a comparatively high latency (latencyis the time it takes from initiation to completion of a data transaction). Frame relay was introduced in the same period. This is a comparatively low latency system.This section provides design data and brief descriptions of wide area data networking as a whole with hypothetical reference circuits, the archetypical data link layer protocol, high‐level data link control (HDLC), X.25 and its companion, link access protocol B‐layer (LAPB), TCP/IP family of protocols, frame relay family of protocols, and a brief description of SMDS (switched multimegabit data service). Variants of LAPD are discussed in the frame relay section of this chapter.

Parallel implementing OpenGL on PVM

In recent years, networked sensors are finding use in a variety of different applications ranging from temperature monitoring to battlefield strategy planning. Advances in fabrication techniques have led to the development of sensor-actuator devices called MEMS. It has now become possible to move software closer to where the “action” is, i.e. the sensors themselves. These sensor devices typically have a micro-controller, instruction and data memory, a radio module for wireless communication and an operating system. These devices are severely resource constrained in terms of memory, processing power and energy, since most of these devices are battery driven. A sensor network consists of a number of sensors spread across a geographical area. Each sensor has wireless communication capability and sufficient intelligence for signal processing and networking of the data. In this paper, we discuss a mechanism to achieve prioritized task scheduling in TinyOS. We investigate into the details of how the task scheduling is currently done in TinyOS and the adverse effects that this could cause. We show use-cases where certain ”important” tasks could be given less preference when compared to other ”notso-important” tasks. We propose a new mechanism at the programming model level to introduce the concept of priority for a task and explain how the scheduling module has to be changed to enforce this priority scheme. Finally, we show empirical results to justify our solution.

This chapter presents a compositional theory of networking as an example of a useful and realistic domain theory. First, it uses networking to illustrate all the parts of a domain theory, including a reusable domain description with intrinsic state and behavior, software interfaces and specifications, requirements, proof obligations, and theorems. Next, the theory is extended with composition of network domains, which is directly relevant to solving today’s most critical networking problems. Finally, the chapter proposes ways in which the theory can contribute directly to the design and development of network software.

The centralized system approach for computer and telecommunication network management has been presenting scalability problems along with the growth in the amount and diversity of managed equipment. Moreover, the increase in complexity of the services being offered through the networks also contributes to adding extra workload to the management station. The amount of data that must be handled and processed by only one administration point could lead to a situation where there is not enough processing and storage power to carry out an efficient job. In this work we present an alternative approach by creating a highly distributed computing environment through the use of Grids of autonomous agents to analyze large amounts of data, which reduce the processing costs by optimizing the load distribution and resource utilization. Copyright © 2004 John Wiley & Sons, Ltd.