2104066
Design and evaluation of a resource selection framework for Grid applications
While distributed, heterogeneous collections of computers ("Grids") can in principle be used as a computing platform, in practice the problems of first discovering and then organizing resources to meet application requirements are difficult. We present a general-purpose resource selection framework that addresses these problems by defining a resource selection service for locating Grid resources that match application requirements. At the heart of this framework is a simple, but powerful, declarative language based on a technique called set matching, which extends the Condor matchmaking framework to support both single-resource and multiple-resource selection. This framework also provides an open interface for loading application-specific mapping modules to personalize the resource selector. We present results obtained when this framework is applied in the context of a computational astrophysics application, Cactus. These results demonstrate the effectiveness of our technique.
10496869
Conservative Scheduling: Using Predicted Variance to Improve Scheduling Decisions in Dynamic Environments
In heterogeneous and dynamic environments, efficient execution of parallel computations can require mappings of tasks to processors whose performance is both irregular (because of heterogeneity) and time-varying (because of dynamicity). While adaptive domain decomposition techniques have been used to address heterogeneous resource capabilities, temporal variations in those capabilities have seldom been considered. We propose a conservative scheduling policy that uses information about expected future variance in resource capabilities to produce more efficient data mapping decisions. We first present techniques, based on time series predictors that we developed in previous work, for predicting CPU load at some future time point, average CPU load for some future time interval, and variation of CPU load over some future time interval. We then present a family of stochastic scheduling algorithms that exploit such predictions of future availability and variability when making data mapping decisions. Finally, we describe experiments in which we apply our techniques to an astrophysics application. The results of these experiments demonstrate that conservative scheduling can produce execution times that are both significantly faster and less variable than other techniques.
11280884
A novel cache design for vector processing
This paper introduces an innovative cache design for vector computers, called prime-mapped cache. By utilizing the special properties of a Mersenne prime, the new design does not increase the critical path length of a processor, nor does it increase the cache access time as compared to a direct-mapped cache. The prime-mapped cache minimizes cache miss ratio caused by line interferences that have been shown to be critical for numerical applications by previous investigators. We show that significant performance gains are possible by adding the proposed cache memory into an existing vector computer provided that application programs can be blocked. The performance gain will increase with the increase of the speed gap between processors and memories. We develop an analytical performance model based on a generic vector computation model to study the performance of the design. Our preliminary performance analysis on various vector access patterns shows that the prime-mapped cache can provide as much as a factor of 2 to 3 performance improvement over the conventional direct-mapped cache in the vector processing environment. Moreover, the additional hardware cost introduced by the new mapping scheme is negligible.
3410538
A Flexible Context-Aware Authorization Framework for Mediation Systems
Security is a critical concern for mediator-based data integration among heterogeneous data sources. This paper provides a modeling and architectural solution to the problem of mediation security that addresses the security challenges including context-awareness, semantic heterogeneity, and multiple security policy specification. A generic, extensible modeling method for the security policies in mediation systems is presented. A series of authorization constraints are identified based on the relationship on the different security components in the mediation systems. Moreover, we enforce the flexible access control to mediation systems while providing uniform access for heterogeneous data sources.
15362390
Transforming Sem-ODM semantic schemas to DTDs
Exporting data in traditional databases as XML documents so that non-XML data can be accessed and exchanged seamlessly among applications has been studied in a number of projects. In this paper, we present an algorithm that automatically derives a Document Type Definition (DTD) from a Semantic Schema of the Semantic Binary Object-Oriented Data Model (Sem-ODM) based on the formal definitions of DTDs and Semantic Schemas. The structure and semantic information of a Semantic Schema is captured and expressed naturally in a DTD without applying any complicated operators or scanning the actual data stored in the database. Furthermore, the formalization of the two schemas connects the two data models and helps us better understand the capabilities brought about by publishing Sem-ODB data as XML.
8188037
Performance evaluation of distributed-antenna communications systems using beam-hopping
Digital beamforming (DBF) techniques are capable of improving the performance of communications systems significantly. However, if the transmitted signals are conflicted with strong interference, especially, in the direction of the transmitted beams , these directional jamming signalswill severely degrade the system performance. In order to efficiently mitigate the interference of the directional jammers, in this contribution a beam-hopping (BH) communications scheme is proposed. In the proposed BH communications scheme, only one pair of the beams is used for transmission and it hops from one to the next according to an assigned BH pattern. In this contribution a range of expressions in terms of the average SINR performance have been derived, when both the uplink and downlink are considered. The average SINR performance of the proposed BH scheme and that of the conventional single-beam (SB) as well as multiple-beam (MB) assisted beam-processing schemes have been investigated. Our analysis and results show that the proposed BH scheme is capable of efficiently combating the directional jamming, with the aid of utilizing the directional gain of the beams generated by both the transmitter and the receiver. Furthermore, the BH scheme is capable of reducing the intercept probability of the communications. Therefore, the proposed BH scheme is suitable for communications, when several distributed antenna arrays are available around a mobile.
3393163
Dynamic Integration Strategy for Mediation Framework
The trend in the information area is to provide integrated access to diverse and dynamic information sources. We present a modeling and architectural solution to the problem of data integration from heterogeneous data sources based on the use of wrappers and mediators. The mediator supports integrated query processing by the semantic mapping between the global schema type and the local schema types. However, mediation poses extensive security problems. Protecting proprietary data from unauthorized access is recognized as one of the most significant barriers to the mediation systems. Our approach benefits in both flexible strategy of data integration based on semantic mappings and dynamic access control in mediation systems.