I n to&y ' s world of computers, deuling with huge cirnounts qf dutu is riot unusual. The need to distribute this datu in order to increuse its uvuilubility and iricreuse the perfii,rmance of accessing it is more urgent than ever: Fbr these reasons it is necessary to develop scalable distrihmd &tu structures. h. this paper we propose EH*, a rli.vtributedvariant of the Extendible Hushing data structure. It con.vists qf buckets of data thut ure spreud kcross multiple servers and autonomous clients thut can acces:r these buckets in parallel. E H * is sculable in the sense thut it grows grcicefully, one bucket at U time, to LL large number ofservers. The communication overhead is re1utivel:v independent of the number qf servers and clients in the system. EH * oflers U high query eficiency und good storuge spuce utiliztrtiori.. Tlze simulution results reveal thut the method is cumptrrul?le to the L H * introduced by Witold Litwin.
Various methods have been proposed f o r building faulttolerant software in an effort to provide substantial improvements in software reliability f o r critical applications, such as jlight control, air-trajic control, patient monitoring, or power plant monitoring. The two best-known methods of building fault-tolerunt software are n-version programming and recovery blocks. To tolerate faults, both of these techniques rely on design diversity, i.e., the availability of multiple implementations of a specification. Software engineers assume that the different implementations use different designs and, thereby, it is hoped, contain different faults.Our study uses a novel method of incorporating diversity in the development of one version of the software. We term this approach the pipeline method of software development. Its purpose is to eliminate as many software faults as possible before the testing phase. The method was applied to the speciJcation of a real, automatic airplane-landing problem. The results of the pipeline development method are presented.
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