After many years of studies, efficient data cube computation remains an open field of research due to ever-growing amounts of data. One of the most efficient algorithms (quotient cubes) is based on the notion of cube ...
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After many years of studies, efficient data cube computation remains an open field of research due to ever-growing amounts of data. One of the most efficient algorithms (quotient cubes) is based on the notion of cube cells closure, condensing groups of cells into equivalence classes, which allows to loss lessly decrease amount of data to be stored. Recently developed parallel computation framework Map-Reduce lead to a new wave of interest to large-scale algorithms for data analysis (and to so called cloud-computing paradigm). This paper is devoted to applying such approaches to data and computation intensive task of OLAP-cube computation. We show that there are two scales of Map-Reduce applicability (for local multicore or multiprocessor server and multi-server clusters), present cube construction and query processing algorithms used at the both levels. Experimental results demonstrate that algorithms are scalable.
Decompilation is reconstruction of a program in a highlevel language from a program in a low-level language. In most cases static decompilation is unable to completely reconstruct high-level data types due to loss of ...
Element constructor is one of most expensive operations of the XQuery language as it requires deep copy of the nodes which make up the content of the constructed element. In this paper we propose various optimization ...
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Element constructor is one of most expensive operations of the XQuery language as it requires deep copy of the nodes which make up the content of the constructed element. In this paper we propose various optimization and implementation techniques to avoid copying of the nodes during constructor evaluation. The proposed techniques are based on using special kind of XQuery constructors with modified semantics which evaluation does not require content node copying. We also provide optimization rules which replace standard constructors with modified ones without changing query result. The proposed techniques are designed to minimize modifications of an existing implementation. Possible technique extensions which might depend on implementationspecific features are also considered. We present results from experimental study of the techniques which demonstrate performance improvement of constructor evaluation.
Contemporary commodity operating systems are too big and do not inspire trust in their security and reliability. Still they are used for processing sensitive data due to the vast amount of legacy software and good sup...
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ISBN:
(纸本)9781605584737
Contemporary commodity operating systems are too big and do not inspire trust in their security and reliability. Still they are used for processing sensitive data due to the vast amount of legacy software and good support for virtually all hardware devices. Common approaches used to ensure sensitive data protection are either too strict or not reliable. In this article we propose virtualization-based approach for preventing sensitive data leaks from a computer running untrusted commodity OS without sacrificing public network connectivity, computer usability and performance. It is based on separating privileges between two virtual machines: public VM that has unlimited network access and private (isolated) VM that is used for processing sensitive data. Virtual machine monitor uses public VM to provide transparent access to Internet for selected trusted applications running inside the private VM on a system call level. Proposed security architecture allows using one and the same untrusted OS on both virtual machines without necessity to encrypt sensitive data. However it poses a challenge of enforcing dynamic protection over the trusted applications running in the potentially compromised OS. We investigate this problem and provide our solution for it. Copyright 2009 ACM.
Write-then-read transaction (W\R) is a transaction that consists of two consecutive phases: write phase containing write and read operations in random order, and second phase containing read operations and write opera...
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Write-then-read transaction (W\R) is a transaction that consists of two consecutive phases: write phase containing write and read operations in random order, and second phase containing read operations and write operations only on data items previously updated in the first phase. W\R transactions are of great practical importance, but the problem of efficient processing of such transactions has received only little attention of research community so far. In this paper, we present Dynamic Versioning Protocol (DVP), which optimizes W\R transactions processing using versions on the second phase. DVP supports STEAL policy and incorporates dynamic approach to the problem of selecting most suitable versions for read operations of the read phase. We prove the correctness of our protocol, so it guarantees the serializability of all transactions. The conducted experimental evaluation shows significant benefits of DVP for processing of concurrent W\R transactions.
Several native approaches to storing large XML data sets exist. In all of these approaches the internal data representation is designed to support any ad-hoc XQuery query. In this paper we argue that XQuery and its da...
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Several native approaches to storing large XML data sets exist. In all of these approaches the internal data representation is designed to support any ad-hoc XQuery query. In this paper we argue that XQuery and its data model are too universal and any one-size-fits-all XML representation leads to significant overheads in terms of representation size and complexity. Based on the consideration that in many applications queries/updates workload is known in advance and does not change often, we propose an application-tailored XML storage. Elimination of the superfluous XQuery data model features and utilization of the various physical data representations improve performance on the specified workload, while ad-hoc queries support can be limited.
Cross toolkits (assembler, linker, debugger, simulator, profiler) are widely used for software-hardware codesign;an early creation of cross toolkits is an important success factor for industrial embedded systems. At t...
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Cross toolkits (assembler, linker, debugger, simulator, profiler) are widely used for software-hardware codesign;an early creation of cross toolkits is an important success factor for industrial embedded systems. At the hardware design stage systems are subject to significant design alterations including changes in the instruction set of target CPUs. This is a challenging issue for early cross toolkit development. In this paper, we present a new Architecture Description Language (ADL) called ISE language and an approach to early cross toolkit development to cope with hardware design changes. The paper introduces the MetaDSP framework that supports ISE-based construction of cross toolkits and gives brief overview of the MetaDSP applications to industrial projects that proves the industrial strength of the presented approach and tools.
We present an automatic method, named SemaTESK, for generation of test sets for a translator front end. We focus on the validation and verification of static semantics checker. Most the know methods for semantics test...
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In this paper we describe a method for simulation-based verification of microprocessor units based on cycle-accurate contract specifications. Such specifications describe behavior of a unit in the form of precondition...
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Formal methods (FM) are being actively developed nowadays. Still they find little use even in the target industry domains that require high quality, robust and standard-conforming software. Some of the difficulties in...
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Formal methods (FM) are being actively developed nowadays. Still they find little use even in the target industry domains that require high quality, robust and standard-conforming software. Some of the difficulties in FM utilization are caused by unique characteristic features of the new Innovation Economy such as constantly growing number of new domains and technologies that calls for more and more experts who generate and possess knowledge. It is the knowledge formalization that is the prerequisite for FM application. This paper discusses features of the Innovation Economy that challenge FM practical use, considers positive cases of industrial applications of *** upon the analysis of those cases we suggest shifting the focus of FM development and extension to close cooperation with problem area experts and to promotion of the formalized approaches, techniques,and notations as interface language between problem areas and IT specialists.
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