31591898
Scanning the issue - special issue on real-time systems
8777661
Adaptive transaction routing in a heterogeneous database environment
The issue of transaction routing in a heterogeneous database environment is examined where transaction characteristics like reference locality implies that certain processing systems can be identified as being, in general, more suitable than others for a given transaction class. Routing which ignores these distinctions in an attempt to balance system load can degrade system performance. An adaptive routing strategy is considered which: (1) estimates the response time based on a steady-state analysis; (2) monitors how well actual response time conforms to the estimate; and (3) adaptively adjusts future estimates through a feedback control based on (2). It is found that the adaptive strategy greatly enhances performance robustness as compared to the results of the strategy without feedback. The feedback process used alleviates the sensitivity to accurate estimations of workload and system parameters. Various simulation studies are used to illustrate the adaptive strategy's robustness.<<ETX>>
11078936
Software architecture supporting integrated real-time systems
To achieve reliability, reusability, and cost reduction, a significant trend in building large complex real-time systems is to integrate separate application modules of different criticalities in a common hardware platform. An essential requirement of integrated real-time systems is to guarantee spatial and temporal partitioning among applications in order te ensure an exclusive access of physical and temporal resources to the applications. In this paper we propose software architecture, implemented as SPIRIT-µKernel, for strongly partitioned integrated real-time systems. The SPIRIT-µKernel has been designed and implemented based on a two-level hierarchical scheduling methodology such that the real-time constraints of each application can be guaranteed. To demonstrate the feasibility of the SPIRIT-µKernel, we have ported two real-time operating systems (RTOS), WindRiver's VxWorks and Cygnus's eCos, on the top of the microkernel. Thus, different RTOS can be applied in various partitions to provide required features for each application. Based on the measured performance results, the SPIRIT-µKernel architecture is practical and appealing due to its low overheads of kernel services and the support for dependable integration of real-time applications via scheduling algorithm.
40618061
Transaction Recovery in Distributed DB/DC Systems: A Progressive Approach
10753893
Evaluation of Error Recovery Blocks Used for Cooperating Processes
Three alternatives for implementing recovery blocks (RB's) are conceivable for backward error recovery in concurrent processing. These are the asynchronous, synchronous, and the pseudorecovery point implementations. Asynchronous RB's are based on the concept of maximum autonomy in each of concurrent processes. Consequently, establishment of RB's in a process is made independently of others and unbounded rollback propagations become a serious problem. In order to completely avoid unbounded rollback propagations, it is necessary to synchronize the establishment of recovery blocks in all cooperating processes. Process autonomy is sacrificed and processes are forced to wait for commitments from others to establish a recovery line, leading to inefficiency in time utilization. As a compromise between asynchronous and synchronous RB's we propose to insert pseudorecovery points (PRP's) so that unbounded rollback propagations may be avoided while maintaining process autonomy. We developed probabilistic models for analyzing these three methods under standard assumptions in computer performance analysis, i.e., exponential distributions for related random variables. With these models we have estimated 1) the interval between two successive recovery lines for asynchronous RB's, 2) mean loss in computation power for the synchronized method, and 3) additional overhead and rollback distance in case PRP's are used.
17765159
VLSI Circuit Testing Using an Adaptive Optimization Model
The purpose of testing is to determine the correctness of the unit under test in come optimal way. One difficulty in meeting the optimality requirement is that the stochastic properties of the unit are usually unknown a priori. For instance, one might not know exactly the yield of a VLSI production line before one tests the chips made as a result. Given the probability of unit failure and the coverage of a test, the optimal test period is easy to obtain. However, the probability of failure is not usually known a priori. We therefore develop an optimal sequential testing strategy which estimates the production yield based on ongoing test results, and then use it to determine the optimal test period.
7326399
A Scalable Update Management Mechanism for Query Result Caching Systems at Database-Driven Web Sites
A key problem in using caching technology for dynamic contents lies in update management. An update management scheme should be very efficient without imposing much extra burden to the system, especially to the original database server. We propose an scalable update management mechanism for query result caching in database-backed Web sites. Our mechanism employs a two-phase consistency checking method, which prunes out unaffected queries at the earliest possible moment. The method scales well with a high number of cached instances.
12566781
Web-Based Simulation with Server Application Approach under Distributed Environment
2576924
Integration of 802.11 and third-generation wireless data networks
The third-generation (3G) wide area wireless networks and 802.11 local area wireless networks possess complementary characteristics. 3G networks promise to offer always-on, ubiquitous connectivity with relatively low data rates. 802.11 offers much higher data rates, comparable to wired networks, but can cover only smaller areas, suitable for hot-spot applications in hotels and airports. The performance and flexibility of wireless data services would be dramatically improved if users could seamlessly roam across the two networks. In this paper, we address the problem of integration of these two classes of networks to offer such seamless connectivity. Specifically, we describe two possible integration approaches - namely tight integration and loose integration and advocate the latter as the preferred approach. Our realization of the loose integration approach consists of two components: a new network element called IOTA gateway deployed in 802.11 networks, and a new client software. The IOTA gateway is composed of several software modules, and with cooperation from the client software offers integrated 802.11/3G wireless data services that support seamless intertechnology mobility, Quality of Service (QoS) guarantees and multiprovider roaming agreements. We describe the design and implementation of the IOTA gateway and the client software in detail and present experimental performance results that validate our architectural approach.
15368609
Data quality in context
ATA-QUALITY (DQ) PROBLEMS ARE INCREASINGLY EVIdent, particularly in organizational databases. Indeed, 50% to 80% of computerized criminal records in the U.S. were found to be inaccurate, incomplete, or ambiguous. The social and economic impact of poor-quality data costs billions of dollars. [5-7, 10]. Organizational databases, however, reside in the larger context of information systems (IS). Within this larger context, data is collected from multiple data sources and stored in databases. From this stored data, useful information is generated for organizational decision-making. A new study reveals businesses are defining data quality with the consumer in mind.
23745663
A filtering method for searching similar multidimensional sequences under the time-warping distance
The filtering method is currently the most suitable approach for the fast retrieval of similar sequences under the time-warping distance. Several filtering methods under the time-warping distance have been proposed, but they are only for real number sequences. This paper presents an efficient filtering method for the retrieval of similar multidimensional sequences. First, we propose three basic filtering measures (the end-point distance, the min-region distance, and the interim time-warping distance) based on the ones appeared in the literature, and one of their direct combinations (the point-region distance). Next, we investigate their problems with a large number of multidimensional sequences. In order to alleviate those problems, we extend the end-point distance and the min-region distance into the extended end-point distance and the segmented min-region distance, respectively, and combine them into a novel measure, the extended point-region distance. A multi-step architecture is adopted to implement the retrieval process with the proposed measure. Experiments with synthetic sequences are conducted for the performance comparison.