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事物随时间变化的特性广泛存在,在其属性的特征值上存在着大量时态数据。然而关系数据库由于关系模型本身限制,基于关系的时态信息处理难以有效表示时态对象复杂的数据结构,不具备直接的时态数据管理能力。以简易的人事信息管理系统为例,对基于关系数据库的时态数据存取进行了探讨。 相似文献
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主要阐述时态数据库在发展过程中,特别是近几年的发展过程中所形成的较一般的,为广大在数据库领域研究的专家、学者所认同的,并在进一步发展的时态数据库模型、技术和遇到的困难等. 相似文献
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时态数据库中间件的设计与实现 总被引:1,自引:0,他引:1
时态数据库理论研究取得了丰富的成果,但是时态数据库实现技术尚处于发展阶段.在总结前人工作的基础上,讨论了时态数据库中间件平台的实现难点、选择ATSQL2的原因、整体架构、语法和语义处理算法等内容;采用符合当前现实条件的中间件形式,实现了一个基于ATSQL2的时态数据库平台. 相似文献
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能为时态数据库设计出一种比现有的时态索引技术更健全且更有效的索引技术是当今时态数据库研究的主要问题,本文结合2R-tree索引、GR-tree索引和G4R-tree索引,提出了一种新的索引技术,称为G2R-tree索引。它能有效地处理所有类型的双时态数据,而且性能与4R-tree索引和GR-tree索引相当。 相似文献
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基于BCDM的双时态关系代数 总被引:10,自引:0,他引:10
双时态概念数据模型BCDM是一种重要的时态数据库模型,基于BCDM模型,建立了一种双时态关系代数.首先,对时态数据库事务时间和有效时间进行规范化的定义,给出BCDM中时间元素的规范化定义和演算描述;而后,定义时态映射,用以描述BCDM中的双时态元组,并形式描述时态映射的演算;最后,用时态映射定义的元组对双时态关系进行定义,并由此给出双时态关系代数运算的形式化描述. 相似文献
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本文讨论了若干时态关系数据库实践中最基本的问题,特别是对一些悬而未决的基本问题,阐述了自己的观点,给出了一些方向性的建议,提出了一个时态关系数据库的基本框架。本文将对时态关系数据库的进一步研究提供了一个基点,对时态数据库基本框架的建立具有一定的帮助作用。 相似文献
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一种基于时态中间件的高效双时态索引模型 总被引:1,自引:0,他引:1
当前的时态数据库中间件不支持包含事务时间和有效时间的双时态数据索引,通过使用适当的数据变换和查询变换,可将双时态数据转化为R树可索引的数据.基于4R技术,提出了作为时态中间件TimeDB组件的双时态索引模型B4Rindex.实验证明,利用该模型对双时态数据进行索引是高效的. 相似文献
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Java 3D实现VRML浏览器新途径 总被引:4,自引:1,他引:4
Java是一种网络语言,Java 3D是Java语言在三维图形领域的扩充,它继承了Java许多优良的特性,Java3D能实现VRML绘制的所有三维图形,通过对Java 3D实现编译浏览VRML文件的分析,简要叙述了Java 3D的几何形体绘制、动画、交互技术,介绍了用Java语言编译VRML文件中遇到的一些技术问题。 相似文献
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In this paper, a new approach to deal with textual attributes in databases is presented. The basic idea is to give a new representation for these attributes, so that it allows us to treat them together with and in the same way than the other database attributes in querying, data warehousing, data mining processes, etc. Additionally, the transformation process of the textual attribute implies the obtaining of a global representation, which includes a great part of the attribute meaning. Moreover, this representation can be improved by using an ontology during the querying process, which enables the semantic queries. The formal representation model is presented in the paper, as well as the mathematical bases for dealing with it. The whole implementation process is also described by using a medical database to show the experimental results. Finally, a set of semantic query examples are offered to explain the advantages of this new approach. 相似文献
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When learning from very large databases, the reduction of complexity is extremely important. Two extremes of making knowledge discovery in databases (KDD) feasible have been put forward. One extreme is to choose a very simple hypothesis language, thereby being capable of very fast learning on real-world databases. The opposite extreme is to select a small data set, thereby being able to learn very expressive (first-order logic) hypotheses. A multistrategy approach allows one to include most of these advantages and exclude most of the disadvantages. Simpler learning algorithms detect hierarchies which are used to structure the hypothesis space for a more complex learning algorithm. The better structured the hypothesis space is, the better learning can prune away uninteresting or losing hypotheses and the faster it becomes.We have combined inductive logic programming (ILP) directly with a relational database management system. The ILP algorithm is controlled in a model-driven way by the user and in a data-driven way by structures that are induced by three simple learning algorithms. 相似文献
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As an alternative to approaches based on entropy and information gain, we describe a system that uses a measure called the impurity level. The learning algorithm based on this measure, which we call FARNI, first induces fuzzy decision trees by using an impurity-level extension for selecting the best branch. This is similar to the way C4.5 and ARNI induce selections for crisp databases. Once FARNI calculates the fuzzy decision tree, it returns compact fuzzy rule sets that apply a pruning process 相似文献
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A General Approach to Clustering in Large Databases with Noise 总被引:8,自引:1,他引:8
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Elisa Bertino Ahmed K. Elmagarmid Mohand-Saïd Hacid 《Multimedia Tools and Applications》2004,23(2):75-101
Quality of Service (QoS) is defined as a set of perceivable attributes expressed in a user-friendly language with parameters that may be objective or subjective. Objective parameters are those related to a particular service and are measurable and verifiable. Subjective parameters are those based on the opinions of the end-users. We believe that quality of service should become an integral part of multimedia database systems and users should be able to query by requiring a quality of service from the system. The specification and enforcement of QoS presents an interesting challenge in multimedia systems development. A deal of effort has been done on QoS specification and control at the system and the network levels, but less work has been done at the application/user level. In this paper, we propose a language, in the style of constraint database languages, for formal specification of QoS constraints. The satisfaction by the system of the user quality requirements can be viewed as a constraint satisfaction problem, and the negotiation can be viewed as constraint optimization. We believe this paper represents a first step towards the development of a database framework for quality of service management in video databases. The contribution of this paper lies in providing a logical framework for specifying and enforcing quality of service in video databases. To our knowledge, this work is the first from a database perspective on quality of service management. 相似文献
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An Approach to Handling Incomplete Information in Databases 总被引:1,自引:0,他引:1