基于遗传算法的分布式异构数据库的查询优化

对于分布武异构数据库，查询优化问题是其核心问题。本文用基于位、值结构树型编码的遗传算法对分布武异构数据库进行查询优化，取得了很好的效果。     

防止利用ODBC技术非法获取企业数据库中重要数据

ODBC和Query技术相结合使得非计算机专业人员不需要编程技术就可以在Excel中直接获取有关数据库的数据，此方法的使用能使非授权人员避开应用系统对他合法性检查，获取企事业单位中某些数据库重要的数据。本文从技术层面上介绍了Access、FoxPro关系数据库的安全隐患以及防范的对策。     

基于数据流的近似查询计算及其应用研究

通过分析基于实化聚集视图的查询重写方法，将相关的查询计算理论与数据流的查询相结合，针对数据流的特征，给出了一种具有广泛应用前景的基于数据流的近似查询计算方案。     

VFP下纯中文万能查询类的实现

Visual Foxpro5．0提供了一个通用查询类，这个类对数据的一致性和可用性都作了准确的判断和处理，但该类为英文版且最多只能进行两个条件的组合查询，本文将它改进为纯中文任意多个条件的组合查询类。     

An interactive agent-based system for concept-based web search

Search engines are useful tools in looking for information from the Internet. However, due to the difficulties of specifying appropriate queries and the problems of keyword-based similarity ranking presently encountered by search engines, general users are still not satisfied with the results retrieved. To remedy the above difficulties and problems, in this paper we present a multi-agent framework in which an interactive approach is proposed to iteratively collect a user's feedback from the pages he has identified. By analyzing the pages gathered, the system can then gradually formulate queries to efficiently describe the content a user is looking for. In our framework, the evolution strategies are employed to evolve critical feature words for concept modeling in query formulation. The experimental results show that the framework developed is efficient and useful to enhance the quality of web search, and the concept-based semantic search can thus be achieved.     

基于中文文本分类的分词方法研究

文本分类有助于用户有选择地阅读和处理海量文本,因此其预备工作分词系统的研究是很有意义的。该文主要提出了一种基于中文文本分类的分词方法,区别于常用的基于字符串匹配等方法,并利用数据库特有的查询技术设计和实现了该分词系统,旨在通过新的分词方法提供更加准确的分词率,同时提高系统实现效率。     

数据挖掘语言研究现状及发展

论文介绍了目前比较流行的几种数据挖掘语言及其标准化方面的研究进展,比较分析了几种数据挖掘语言的优缺点,并对这几种数据挖掘语言的结构和组成进行了探讨和研究,最后探讨了数据挖掘语言的发展趋势,以及需要解决的问题。     

Enhanced abstract data types in object-relational databases

The explosion in complex multimedia content makes it crucial for database systems to support such data efficiently. This paper argues that the “blackbox” ADTs used in current object-relational systems inhibit their performance, thereby limiting their use in emerging applications. Instead, the next generation of object-relational database systems should be based on enhanced abstract data type (E-ADT) technology. An (E-ADT) can expose the semantics of its methods to the database system, thereby permitting advanced query optimizations. Fundamental architectural changes are required to build a database system with E-ADTs; the added functionality should not compromise the modularity of data types and the extensibility of the type system. The implementation issues have been explored through the development of E-ADTs in Predator. Initial performance results demonstrate an order of magnitude in performance improvements. Received January 1, 1998 / Accepted May 27, 1998     

Towards an algebraic theory of information integration

Information integration systems provide uniform interfaces to varieties of heterogeneous information sources. For query answering in such systems, the current generation of query answering algorithms in local-as-view (source-centric) information integration systems all produce what has been thought of as “the best obtainable” answer, given the circumstances that the source-centric approach introduces incomplete information into the virtual global relations. However, this “best obtainable” answer does not include all information that can be extracted from the sources because it does not allow partial information. Neither does the “best obtainable” answer allow for composition of queries, meaning that querying a result of a previous query will not be equivalentto the composition of the two queries. In this paper, we provide a foundation for information integration, based on the algebraic theory of incomplete information. Our framework allows us to define the semantics of partial facts and introduce the notion of the exact answer—that is the answer that includes partial facts. We show that querying under the exact answer semantics is compositional. We also present two methods for actually computing the exact answer. The first method is tableau-based, and it is a generalization of the “inverse-rules” approach. The second, much more efficient method, is a generalization of the rewriting approach, and it is based on partial containment mappings introduced in the paper.     

Zoned-partitioning of tree-like access methods

The performance of access methods and the underlying disk system is a significant factor in determining the performance of database applications, especially with large sets of data. While modern hard disks are manufactured with multiple physical zones, where seek times and data transfer rates vary significantly across the zones, there has been little consideration of this important disk characteristic in designing access methods (indexing schemes). Instead, conventional access methods have been developed based on a traditional disk model that comes with many simplifying assumptions such as an average seek time and a single data transfer rate. The paper proposes novel partitioning techniques that can be applied to any tree-like access methods, both dynamic and static, fully utilizing zoning characteristics of hard disks. The index pages are allocated to disk zones in such a way that more frequently accessed index pages are stored in a faster disk zone. On top of the zoned data placement, a localized query processing technique is proposed to significantly improve the query performance by reducing page retrieval times from the hard disk.