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演绎数据库中的语义查询优化方法 总被引:6,自引:0,他引:6
陶世群 《小型微型计算机系统》1996,17(5):47-52
语义查询优化的目的是使用语义知识来进行有效的查询,以提高查询效率,通过语义编译和语义转换,把一个查询转换成一个或多个更为有效的等价查询。本文介绍在演绎数据库中语义查询优化方法。 相似文献
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查询是数据库的核心操作,随着数据库技术的发展以及数据量急剧增加,对查询性能的要求越来越高,查询优化成为数据库管理系统亟待解决的重要问题。文中针对应用最广泛的SQL Server数据库的查询优化器进行研究。通过图形研究查询优化器的工作原理,并深入分析提交SQL语句、解析、代数化、查询优化、编译、执行、结果等查询优化器的工作步骤;进行实例分析,运用图形表示了逻辑树和经过优化后得到的查询执行计划。结果表明,SQL语句是查询优化的基础,实际应用时需要写出符合查询优化器规则的SQL语句 相似文献
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刘维学 《计算机技术与发展》2013,(11):108-111
查询是数据库的核心操作,随着数据库技术的发展以及数据量急剧增加,对查询性能的要求越来越高,查询优化成为数据库管理系统亟待解决的重要问题。文中针对应用最广泛的SQL Server数据库的查询优化器进行研究。通过图形研究查询优化器的工作原理,并深人分析提交SQL语句、解析、代数化、查询优化、编译、执行、结果等查询优化器的工作步骤;进行实例分析,运用图形表示了逻辑树和经过优化后得到的查询执行计划。结果表明,SQL语句是查询优化的基础,实际应用时需要写出符合查询优化器规则的SQL语句。 相似文献
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在传统的分布式操作系统灾备处理过程的基础上,结合已有分布式跨边界片段连接优化方法,提出基于空间片段拓扑连接优化的关系代数转换原则,通过利用等价转换规则,进一步简化经过数据本地化处理后的查询树。然后引入连接归并树和执行计划树等概念,并利用相应归并和优化算法将全局空间查询转化为各个场地局部空间数据库的具体执行计划。 相似文献
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传统的查询树优化方法,即基于左线性树、右线性树、浓密树、操作森林的并行数据库查询优化方法,各有优劣,对其的研究比较深入、成熟;基于多重加权树的查询优化方法,研究了其并行查询计划模型、并行查询计划的复杂性模型和查询优化算法;语义查询优化方法将一个查询变换成一个或数个语义等价的查询,进而寻找并执行这些等价查询中具有较好实现策略的一个;基于Agent的并行数据库查询优化采用Multi-Agent技术自动查找与给定查询有关的完整性约束条件,使得多个关系间连接操作的效率得到很大的提高;基于遗传算法的并行优化算法,深入研究了基于机群并行数据库中关系存储的选择、多连接查询优化和查询处理等关键技术。 相似文献
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Approaches for indexing proteins and for fast and scalable searching for structures similar to a query structure have important applications such as protein structure and function prediction, protein classification and drug discovery. In this paper, we develop a new method for extracting local structural (or geometric) features from protein structures. These feature vectors are in turn converted into a set of symbols, which are then indexed using a suffix tree. For a given query, the suffix tree index can be used effectively to retrieve the maximal matches, which are then chained to obtain the local alignments. Finally, similar proteins are retrieved by their alignment score against the query. Our results show classification accuracy up to 50% and 92.9% at the topology and class level according to the CATH classification. These results outperform the best previous methods. We also show that PSIST is highly scalable due to the external suffix tree indexing approach it uses; it is able to index about 70,500 domains from SCOP in under an hour. 相似文献
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通过分析已有的索引结构在进行k近邻查询时效率上的不足,提出了适合进行k近邻查询的X*树索引结构,采用了新的结点分裂算法,同时不需要额外存储结点分裂的历史信息。实验结果表明它比X树的时间和空间性能更好,更适合k近邻查询的应用。 相似文献
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在射频识别(RFID)系统中,存在阅读器与多个标签同时通信的碰撞问题,标签防碰撞技术是解决标签碰撞问题、提高标签识别效率的关键技术。在阐述传统二进制查询树算法(QT)的基础上提出了一种改进的查询树标签防碰撞算法-动态二进制查询树算法(DQT)。该算法通过曼彻斯特编码,识别出碰撞位,从而动态改变查询前缀,使阅读器的查询次数与标签的通信量大大减少,提高了标签的识别效率。仿真实验表明,DQT算法在大量标签识别场合下比QT算法更具有效性和稳定性。 相似文献
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Yong Suk Choi 《Data mining and knowledge discovery》2011,22(1-2):211-231
With the public availability of a number of syntactically parsed text corpora, it has been increasingly important to efficiently extract desired information from such corpora. Many conventional works extract a desired text part by matching the parse tree of each sentence to a query that is represented as a structural form of relational predicates expressing a common structural pattern of desired text parts. However, although those works can be useful for limited types of simple queries, they are not very efficient in general because query formulations are sometimes very complicated for complex patterns of desired text parts and query matching tasks are likely to be exponentially time-consuming when considering a variety of complex sentential structures in a text corpus. In order to overcome such inadequacy, we present a novel tree pattern expression (TPE) that can represent various structural patterns intuitively and reduce pattern-matching complexity significantly. This paper first proposes TPE and its pattern-matching algorithm, and then theoretically analyzes the complexity of the proposed pattern-matching algorithm. It also illustrates a TPE-based information extraction system, which is applied to real text mining in a bio-text corpus. It finally shows some experimental results with some discussions in comparison with other systems. 相似文献
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Dimitri Theodoratos Pawel Placek Theodore Dalamagas Stefanos Souldatos Timos Sellis 《The VLDB Journal The International Journal on Very Large Data Bases》2009,18(1):233-254
Nowadays, huge volumes of data are organized or exported in tree-structured form. Querying capabilities are provided through
tree-pattern queries. The need for querying tree-structured data sources when their structure is not fully known, and the
need to integrate multiple data sources with different tree structures have driven, recently, the suggestion of query languages
that relax the complete specification of a tree pattern. In this paper, we consider a query language that allows the partial
specification of a tree pattern. Queries in this language range from structureless keyword-based queries to completely specified
tree patterns. To support the evaluation of partially specified queries, we use semantically rich constructs, called dimension
graphs, which abstract structural information of the tree-structured data. We address the problem of query containment in
the presence of dimension graphs and we provide necessary and sufficient conditions for query containment. As checking query
containment can be expensive, we suggest two heuristic approaches for query containment in the presence of dimension graphs.
Our approaches are based on extracting structural information from the dimension graph that can be added to the queries while
preserving equivalence with respect to the dimension graph. We considered both cases: extracting and storing different types
of structural information in advance, and extracting information on-the-fly (at query time). Both approaches are implemented,
validated, and compared through experimental evaluation. 相似文献
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The problem of answering XML queries using path-based indexes is to find efficient methods for accelerating the XML query
with pre-designed index structures over the XML database. This problem received increasing interests and have been lucubrated
in recent years. Regular path expression is the core of the XML query languages e.g., XPath and XQuery. Most of the state-of-the-art
path-based XML indexes, therefore, hammer at how to efficiently answer the path-based XML queries. This paper surveys various
approaches to indexing XML data proposed in the literature. We give a step by step analysis to show the evolution of index
structures for XML path information, based on tree structures or more commonly, directed labeled graphs. For each approach,
we first present the specific issue it aims to tackle, and then the proposed solution presented. Furthermore, construction,
physical data storage and maintenance costs, are analyzed. 相似文献