On the use of a formal requirements engineering language: The Generalized Railroad Crossing Problem

In this paper, we report on the use of theAlbert II requirements specification language through the handling of the Generalized Railroad Crossing case study. This formal language is based on an ontology of concepts used for capturing requirements inherent in real-time, distributed systems. Because of itsnaturalness, the language supports a direct mapping of customers’ informal needs onto formal statements, without having to introduce artificial elements. The language is founded on a formal framework (real-time temporal logic) which supports the reasoning process of the analyst during the elaboration of the specification. Such support for the reasoning is illustrated in the context of a goal-oriented approach adopted for the elaboration of the case study.     

一种改进的嵌入式实时OS消息机制

分析了基于微内核的嵌入式操作系统中影响消息传递性能的各种因素,从而提出一种改进的消息实现机制,并对这种消息机制的性能、同步性、安全性进行分析。     

An energy-efficient design of microkernel-based on-chip OS for NOC-based manycore system

The chip multiprocessor is the most prolific processor design because its many cores enhance system performance. Network on chip (NOC) has been proposed as a promising model to solve the connection problem of the cores. However, a new challenge consists of fully benefiting from the on-chip network and the cores. In this paper, we propose a novel energy-efficient design of a microkernel-based on-chip operating system for an NOC-based manycore system. The operating system (OS) is partitioned into the microkernel and the other OS modules. They are distributed on the network to provide services to the user programs. Our experimental results show that our design can improve system performance with reduced power consumption.     

Mining generalized temporal patterns based on fuzzy counting

Event-based sequences are a kind of pattern based on temporal associations with two essential characteristics: they are syntactically simple and have a great expressive power. For this reason, event-based sequence mining is an interesting solution to the problem of knowledge discovery in dynamic domains, mainly characterized by a time-varying nature. The inter-transactional model has led to the design of algorithms aimed to obtain this sort of patterns from time-stamped datasets. These algorithms extend the well-known Apriori algorithm, by explicitly adding the temporal context where associations among frequent events occurs. This leads to the possibility of extracting a larger number of patterns with a potential interest in decision making. However, its usefulness is diminished in those datasets where the characteristics of variability and uncertainty are present, which is a common issue in real domains. This is due to the rigidity of the counting method, which uses an exact measure of distance between temporal events. As a solution, we propose a generalization of the temporal mining process, which implies a relaxation of the counting method including the concept of approximate temporal distance between events. In particular, in this paper we present an algorithm, called TSET^fuzzy-Miner, which incorporates a fuzzy-based counting technique in order to extract general, flexible, and practical temporal patterns taking into account the particular characteristics of real domains.     

Unravelling causal and temporal influences underpinning monitoring systems success: A typological approach

This paper is concerned with the causal and temporal underpinnings of information systems success. It uses a typological approach based on fuzzy‐set Qualitative Comparative Analysis and process tracing. It investigates success across multiple cases of information systems adopted for monitoring the disbursement and use of resources within the European Social Fund. The study unravels the causal mechanisms and temporal pathways underpinning success in these systems. It develops a typological theory of monitoring systems success that reveals the temporal pathways embedded within individual cases, as well as broader theoretical patterns emerging across cases. Theoretical, methodological, and practical implications are discussed.     

Beyond Schema Versioning: A Flexible Model for Spatio-Temporal Schema Selection

Schema versioning provides a mechanism for handling change in the structure of database systems and has been investigated widely, both in the context of static and temporal databases. With the growing interest in spatial and spatio-temporal data as well as the mechanisms for holding such data, the spatial context within which data items are formatted also becomes an issue. This paper presents a generalized model that accommodates temporal, spatial and spatio-temporal schema versioning within databases.     

Timed Property Sequence Chart

Property Sequence Chart (PSC) is a novel scenario-based notation, which has been recently proposed to represent temporal properties of concurrent systems. This language balances expressive power and simplicity of use. However, the current version of PSC just represents the order of events and lacks the ability to express timing properties. In real-time systems, it is well known that these timing requirements are very important and need to be specified clearly. Thus, in this paper, we define timed PSC (TPSC) and give the semantics of TPSC in terms of Timed Büchi Automaton (TBA). Then, we measure the expressive power of TPSC based on the recently proposed real-time specification patterns. Finally, we illustrate the use of TPSC in the context of a web service application which requires timing requirements.     

推技术聊天室的研究与实现

分析了客户端拉(Client Pull)方式和服务器推(Server Push)方式两种类型Web聊天室的优劣,并给出了推方式Web聊天室的一种高效的实现方法,在Windows平台上用ISAPI技术实现了一个采用服务器推方式的高性能Web聊天室系统,并探讨了多用户并发访问时的多线程同步安全性设计问题。     

Cherub: Fine-grained application protection with on-demand virtualization

Cherub is an on-demand virtualization mechanism aiming to provide fine-grained application protection in untrusted environments. By leveraging late launch technology, Cherub dynamically inserts a lightweight virtual machine monitor (VMM) under a commodity operating system (OS) when critical pieces of an application code or data are to be processed. The novel design of Cherub with a double-shadowed page table extends VMM level memory protection into application level, such that it can isolate selected memory pages of a target process from the rest and other processes in the same OS environment. With this, Cherub enables fine-grained memory access control and therefore flexible security objectives. Compared to existing approaches, Cherub has the benefits of small code size, low performance overhead, no change to existing applications and commodity OS, and selective protection capability within a single application space. We implement Cherub in Linux and our analysis and evaluation demonstrate its effectiveness and practicality.     

Detection and tracking for robotic visual servoing systems

Robot manipulators require knowledge about their environment in order to perform their desired actions. In several robotic tasks, vision sensors play a critical role by providing the necessary quantity and quality of information regarding the robot's environment. For example, “visual servoing” algorithms may control a robot manipulator in order to track moving objects that are being imaged by a camera. Current visual servoing systems often lack the ability to detect automatically objects that appear within the camera's field of view. In this research, we present a robust “figureiground” framework for visually detecting objects of interest. An important contribution of this research is a collection of optimization schemes that allow the detection framework to operate within the real-time limits of visual servoing systems. The most significant of these schemes involves the use of “spontaneous” and “continuous” domains. The number and location of continuous domains are. allowed to change over time, adjusting to the dynamic conditions of the detection process. We have developed actual servoing systems in order to test the framework's feasibility and to demonstrate its usefulness for visually controlling a robot manipulator.     

实时数据库中具有时态限制的事务调度算法

在实时数据库中，事务对时态数据对象的访问在很多领域的应用日益广泛．目前实时数据库中的事务调度算法大多仅考虑数据的逻辑一致性，而忽略了满足时态的一致性．本文提出了临时数据截止期的概念，以定理的形式证明了低成本的预测算法的可行性，尽可能早地终止或推迟无法满足时态一致性要求的事务的执行，节省了计算资源以供其它事务执行．在此基础上提出了新的实时数据库中具有时态限制的事务调度算法TDDBPA(Temporary Data Deadline—Based Predictive Algorithm)．通过与目前所知的有效算法比较，本算法在性能指标上(事务失败率、浪费的CPU时间)明显优于这些算法．     

Hierarchical clustering: A structure for scalable multiprocessor operating system design

We introduce the concept ofhierarchical clustering as a way to structure shared-memory multiprocessor operating systems for scalability. The concept is based on clustering and hierarchical system design. Hierarchical clustering leads to a modular system, composed of easy-to-design and efficient building blocks. The resulting structure is scalable because it 1) maximizes locality, which is key to good performance in NUMA (non-uniform memory access) systems and 2) provides for concurrency that increases linearly with the number of processors. At the same time, there is tight coupling within a cluster, so the system performs well for local interactions that are expected to constitute the common case. A clustered system can easily be adapted to different hardware configurations and architectures by changing the size of the clusters. We show how this structuring technique is applied to the design of a microkernel-based operating system calledHurricane. This prototype system is the first complete and running implementation of its kind and demonstrates the feasibility of a hierarchically clustered system. We present performance results based on the prototype, demonstrating the characteristics and behavior of a clustered system. In particular, we show how clustering trades off the efficiencies of tight coupling for the advantages of replication, increased locality, and decreased lock contention.     

基于服务体/执行流模型的MiniOSEK操作系统

为解决现有OSEK操作系统实时性不高、效率低等问题,提出了一种新的OSEK操作系统——MiniOSEK。MiniOSEK是建立在服务体／执行流模型的基础上,并符合OSEK／VDX标准规范的嵌入式操作系统。其设计思想是将消息驱动的思想引入到传统OSEK操作系统中,即当一个任务调用OSEK操作系统规范规定的应用程序编程接口（API）函数时,只需要向该接口函数发送一个消息。这样可以减少上下文切换所需的时间,提高嵌入式系统的实时性。     

考虑中断和上下文切换开销的响应时间分析

实时嵌入式系统多采用中断和上下文切换实现多任务间调度,在对此类系统进行可调度性分析时,在任务的最差响应时间计算中必须包含中断和上下文切换开销.现有包含这些开销的方法是将中断作为高优先级任务同时将上下文切换开销加入到任务最差执行时间中进行分析,然而这些方法过于粗略,缺乏对实际系统细节的考虑,计算得到的最差响应时间并不精确.本文首先对中断和上下文切换的机制和时间流程进行详细的阐述,进而分析中断和上下文切换对任务关键性时刻的影响,接着给出包含上述开销的更加精确的响应时间计算方法,最后进行仿真验证.本文扩展了包含系统调度开销的响应时间计算方法,可用于资源受限的硬实时系统中需要精确计算响应时间的场合.     

Specifying real-time properties with metric temporal logic

This paper is motivated by the need for a formal specification method for real-time systems. In these systemsquantitative temporal properties play a dominant role. We first characterize real-time systems by giving a classification of such quantitative temporal properties. Next, we extend the usual models for temporal logic by including a distance function to measure time and analyze what restrictions should be imposed on such a function. Then we introduce appropriate temporal operators to reason about such models by turning qualitative temporal operators into (quantitative) metric temporal operators and show how the usual quantitative temporal properties of real-time systems can be expressed in this metric temporal logic. After we illustrate the application of metric temporal logic to real-time systems by several examples, we end this paper with some conclusions.Part of this research has been performed at the Eindhoven University of Technology when the author was working in ESPRIT project 937: Debugging and Specification of Ada Real-Time Embedded Systems (DESCARTES).     

A survey on temporal logics for specifying and verifying real-time systems

Over the last two decades, there has been an extensive study of logical formalisms on specifying and verifying real-time systems. Temporal logics have been an important research subject within this direction. Although numerous logics have been introduced for formal specification of real-time and complex systems, an up to date survey of these logics does not exist in the literature. In this paper we analyse various temporal formalisms introduced for specification, including propositional/first-order linear temporal logics, branching temporal logics, interval temporal logics, real-time temporal logics and probabilistic temporal logics. We give decidability, axiomatizability, expressiveness, model checking results for each logic analysed. We also provide a comparison of features of the temporal logics discussed.     

基于挖掘具有时态限制数据语义的实时事务调度算法

在实时数据库中,事务对时态数据对象的访问在很多领域的应用日益广泛。目前实时数据库中的事务调度算法大多仅考虑数据的逻辑一致性,而忽略了满足时态的一致性。论文提出了新的实时数据库中具有时态限制的事务调度算法PSBA(PredictionandSimilarity-BasedAlgorithm)。首先提出了临时数据截止期的概念,以定理的形式证明了低成本地预测算法的可行性,尽可能早地终止或推迟无法满足时态一致性要求的事务的执行,节省了计算资源以供其它事务执行。继而通过挖掘数据语义,利用数据相似性,结合预测算法,进一步提高了调度性能。与目前所知的有效算法比较,该算法在性能指标上(事务失败率、浪费的CPU时间)明显优于这些算法。     

An event-based approach for formally verifying runtime adaptive real-time systems

Real-time and embedded systems are required to adapt their behavior and structure to runtime unpredicted changes in order to maintain their feasibility and usefulness. These systems are generally more difficult to specify and verify owning to their execution complexity. Hence, ensuring the high-level design and the early verification of system adaptation at runtime is very crucial. However, existing runtime model-based approaches for adaptive real-time and embedded systems suffer from shortcoming linked to efficiently and correctly managing the adaptive system behavior, especially that a formal verification is not allowed by modeling languages such as UML and MARTE profile. Moreover, reasoning about the correctness and the precision of high-level models is a complex task without the appropriate tool support. In this work, we propose an MDE-based framework for the specification and the verification of runtime adaptive real-time and embedded systems. Our approach stands for Event-B method to formally verify resources behavior and real-time constraints. In fact, thanks to MDE M2T transformations, our proposal translates runtime models into Event-B specifications to ensure the correctness of runtime adaptive system properties, temporal constrains and nonfunctional properties using Rodin platform. A flood prediction system case study is adopted for the validation of our proposal.