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121.
近年来,XML已成为Web上信息交流和资源共享的主要载体。但XML自身的自冗余特性限制了它的普遍应用。目前,已经有研究成果提出了XML的压缩方法。压缩的XML文档能够有效利用存储空间,节省网络带宽。在实际应用中,经常需要对压缩存储的XML文档进行更新。对于大的压缩文档,如果先解压再更新,会消耗大量时间,因此,高效的更新方法应该避免解压缩文档,在压缩的XML文档上直接进行更新操作。本文针对压缩XML文档中的数值类型(包括整型和浮点型)数据,研究了在保持压缩状态条件下如何进行有效的数值更新,提出了基于XPRESS实现的Naive数值更新方法,以及修改XPRESS编码方法实现的更为高效的Pivot数值更新方法。通过大量的实验证明,Pivot数值更新方法不仅能够提供高效的更新处理,而且保持了XPRESS的高压缩率。 相似文献
122.
在数据流上定义了截止期作为连续查询的实时约束,并建立了基于截止期的滑动窗口处理模型;提出了一种基于预测的截止期敏感的滑动窗口处理策略;在多滑动窗口查询处理环境中,提出了一种(k,m )截止期约束机制,在提高查询实时性的前提下,尽可能的满足不同查询对结果丢失率的不同约束。实验结果表明该处理策略能够有效提高数据流上滑动窗口查询的截止期满足率。 相似文献
123.
124.
快速傅立叶变换的应用领域非常广泛,其硬件实现方法多种多样,验证这些电路的正确性具有很强的实用价值。传统的电路正确性验证的方法是模拟,这种方法的主要缺点是随着参与运算的点数的增加,穷尽模拟全部输入情况所耗费的时间越来越长,甚至难以实现。而形式化方法使用纯数学手段证明电路的正确性,克服了传统方法的缺点。首先用重写系统给出了任意N=2M点的基2的流水式快速傅里叶变换处理机的形式化模型,然后给出它的正确性验证,探索了验证处理复数的复杂电路正确性的方法。 相似文献
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126.
Guillem Godoy Hugo Hernández 《Applicable Algebra in Engineering, Communication and Computing》2009,20(2):187-205
Reachability, joinability and confluence properties are known to be undecidable for flat term rewrite systems (TRS). We give
shorter and conceptually simpler proofs of these results. We also prove undecidability of weak normalization and unique normalization
properties for flat TRS.
The first author was supported by Spanish Ministry of Education and Science by the FORMALISM project (TIN2007-66523) and by
the LOGICTOOLS-2 project (TIN2007-68093-C02-01). The second author was supported by Spanish Ministry of Education and Science
by the FORMALISM project (TIN2007-66523). 相似文献
127.
128.
Quang Huy Nguyen Claude Kirchner Hélène Kirchner 《Journal of Automated Reasoning》2002,29(3-4):309-336
This paper presents the design, the implementation, and experiments of the integration of syntactic, conditional possibly associative-commutative term rewriting into proof assistants based on constructive type theory. Our approach is called external because it consists in performing term rewriting in a specific and efficient environment and checking the computations later in a proof assistant. Two typical systems are considered in this work: ELAN, based on the rewriting calculus, as the term rewriting-based environment, and Coq, based on the calculus of inductive constructions as the proof assistant. We first formalize the proof terms for deduction by rewriting and strategies in ELAN using the rewriting calculus with explicit substitutions. We then show how these proof terms can soundly be translated into Coq syntax where they can be directly type checked. For the method to be applicable for rewriting modulo associativity and commutativity, we provide an effective method to prove equalities modulo these axioms in Coq using ELAN. These results have been integrated into an ELAN-based rewriting tactic in Coq. 相似文献
129.
In recent years, researchers have begun to study inductive databases, a new generation of databases for leveraging decision support applications. In this context, the user interacts with the
DBMS using advanced, constraint-based languages for data mining where constraints have been specifically introduced to increase
the relevance of the results and, at the same time, to reduce its volume. In this paper we study the problem of mining frequent
itemsets using an inductive database. We propose a technique for query answering which consists in rewriting the query in
terms of union and intersection of the result sets of other queries, previously executed and materialized. Unfortunately,
the exploitation of past queries is not always applicable. We then present sufficient conditions for the optimization to apply
and show that these conditions are strictly connected with the presence of functional dependencies between the attributes
involved in the queries. We show some experiments on an initial prototype of an optimizer which demonstrates that this approach
to query answering is viable and in many practical cases it drastically reduces the query execution time. 相似文献
130.
Query expansion is a well-known method for improving average effectiveness in information retrieval. The most effective query expansion methods rely on retrieving documents which are used as a source of expansion terms. Retrieving those documents is costly. We examine the bottlenecks of a conventional approach and investigate alternative methods aimed at reducing query evaluation time. We propose a new method that draws candidate terms from brief document summaries that are held in memory for each document. While approximately maintaining the effectiveness of the conventional approach, this method significantly reduces the time required for query expansion by a factor of 5–10. 相似文献