“数据库原理与应用”课程实践教学的改革与探索

"数据库原理与应用"的实践教学是该课程的一个重要教学环节,对提高教学质量和培养学生能力起着决定性的作用。本文论述了该课程在课堂教学、课程设计和课外活动指导三个方面所作的一些实践教学改革和探索,取得了较好的效果。     

Database design practices for inverted files

Database research literature has proposed many procedures, both manual and automated, for database design; selection of secondary indexes for inverted file type database management systems (DBMS) has been repeatedly addressed. The empirical study reported here indicates that practical inverted file design has been relatively unaffected by this research.This paper characterizes the actual database design process used at inverted file DBMS installations along such dimension as: types of secondary keys constructed, the individuals who make index design decisions, the decisions that are changed (and when) after the initial database implementation, the factors that are considered in indexing decisions, and the literature which is used in the process. The study shows that key selection (as one example of a design decision) is addressed by ad hoc procedures and well conceived procedures are not used. Further, the results indicate that database design is dominated by users and systems analysts, indexes are frequently changed and a wide range of database performance and convenience factors are influential in practice. The paper concludes with some recommendations for database design support tools.     

Data mappings again

Extracting data from a relational data base in order to respond to a request for information requires the use of a large number of algorithms. Some of these algorithms are responsible for validating data values, others support the relational operators while others still support the basic data structures used at the lowest levels of the system. This paper recognizes that the successful operation of a relational data base management system is dependent on the organization of these algorithms and emphasizes this point by describing a coherent architecture to embrace them.     

A new approach for estimating null value in relational database

In general, a database system will not operate properly if it exist some null values of attributes in the system. In this paper, we propose a new approach to estimate null values in relational database, which utilize other clustering algorithm to cluster data, and use fuzzy correlation and distance similarity to calculate the correlation of different attribute. For verifying our method, this paper utilize mean of absolute error rate (MAER) as evaluation criterion to compare with other methods; it is shown that our proposed method proves importance than the existing methods for estimating null values in relational database systems.     

Computational methods for database repair by signed formulae*

We introduce a simple and practical method for repairing inconsistent databases. Given a possibly inconsistent database, the idea is to properly represent the underlying problem, i.e., to describe the possible ways of restoring its consistency. We do so by what we call signed formulae, and show how the ‘signed theory’ that is obtained can be used by a variety of off-the-shelf computational models in order to compute the corresponding solutions, i.e., consistent repairs of the database. *This paper is a revised and extended version of [9].     

The complexity of embedded axiomatization for a class of closed database views

It is well known that the complexity of testing the correctness of an arbitrary update to a database view can be far greater than the complexity of testing a corresponding update to the main schema. However, views are generally managed according to some protocol which limits the admissible updates to a subset of all possible changes. The question thus arises as to whether there is a more tractable relationship between these two complexities in the presence of such a protocol. In this paper, this question is addressed for closed update strategies, which are based upon the constant-complement approach of Bancilhon and Spyratos. The approach is to address a more general question – that of characterizing the complexity of axiomatization of views, relative to the complexity of axiomatization of the main schema. For schemata constrained by denial or consistency constraints, that is, statements which rule out certain situations, such as the equality-generating dependencies (EGDs) or, more specifically, the functional dependencies (FDs) of the relational model, a broad and comprehensive result is obtained in a very general framework which is not tied to the relational model in any way. It states that every such schema is governed by an equivalent set of constraints which embed into the component views, and which are no more complex than the original set. For schemata constrained by generating dependencies, of which tuple-generating dependencies (TGDs) in general and, more specifically, both join dependencies (JDs) and inclusion dependencies (INDs) are examples within the relational model, a similar result is obtained, but only within a context known as meet-uniform decompositions, which fails to recapture some important situations. To address the all-important case of relational schemata constrained by both FDs and INDs, a hybrid approach is also developed, in which the general theory regarding denial constraints is blended with a focused analysis of a special but very practical subset of the INDs known as fanout-free unary inclusion dependencies (fanout-free UINDs), to obtain results parallel to the above-mentioned cases: every such schema is governed by an equivalent set of constraints which embed into the component views, and which are no more complex than the original set. In all cases, the question of view update complexity is then answered via a corollary to this main result. Parts of this paper are based upon work reported in [21].     

水土保持监测系统信息平台实现方法(II)——平台更新维护系统

在水土保持监测系统信息平台实现参数库、模型库与数据库分开管理、空间数据与非空间数据集成存储于关系型数据库中的基础上,为了避免数据更新不及时或不完备而造成数据信息过时,导致信息平台变成死库,需要信息平台更新维护系统。基于这一目标,文章集中探讨了信息平台管理维护系统的结构、功能、实现方法和关键技术。其中系统结构在信息平台服务结构基础上采用C/S模式;开发平台采用ArcGIS桌面产品,以对象COM组件技术ArcObjects为平台、MicroSoftVisualBasic为开发环境,进行二次开发。从而集后台数据库和前端数据管理、更新维护于一体而实现了水土保持监测系统信息平台,也为水土保持监测系统成功运行奠定了坚实的基础。     

基于CSCW的异构数据库集成管理研究

CSCW技术有效地改善了人们的工作效率。本文通过分析多数据库协同工作的机制及特性,提出了一个基于CSCW的异构数据库集成管理模型,并在该模型基础上开发了一个企业信息管理原型系统,该系统使用Web Services和XML技术来实现异构数据库系统的协同工作,较好解决了异构数据库集成管理中存在的几个问题。     

PMC: Select Materialized Cells in Data Cubes

QC-Tree is one of the most storage-efficient structures for data cubes in an MOLAP system. Although QC-Tree can achieve a high compression ratio, it is still a fully materialized data cube. In this paper, an improved structure PMC is presented allowing us to materialize only a part of the cells in a QC-Tree to save more storage space. There is a notable difference between our partially materialization algorithm and traditional materialized views selection algorithms. In a traditional algorithm, when a view is selected, all the cells in this view are to be materialized. Otherwise, if a view is not selected, all the cells in this view will not be materialized. This strategy results in the unstable query performance. The presented algorithm, however, selects and materializes data in cell level, and, along with further reduced space and update cost, it can ensure a stable query performance. A series of experiments are conducted on both synthetic and real data sets. The results show that PMC can further reduce storage space occupied by the data cube, and can shorten the time to update the cube.     

利用JSP和ODBC技术实现网络数据库操作应用

目前互联网技术飞速发展,受人瞩目,因此采用何种技术实现网络数据库显得尤为重要。通过对JSP与ASP访问数据库技术进行对比研究,文章采用了JSP和ODBC结合实现网络数据库的方法,并给出了网络数据库交换程序实例。