城市供水管网爆管和折管数据库管理系统的设计与实现

以Visual Basic语言为平台,利用其数据访问特性,开发了城市供水管网爆管、折管数据库管理系统.阐述了系统的设计思想、总体架构以及具体功能的设计与实现.该系统不仅能够对爆管、折管的事故数据进行分类检索与查询,还能同时生成相应的分析图形与报表,对于管网事故管理工作是一种便捷有效的辅助工具.     

MeDEA: A database evolution architecture with traceability

One of the most important challenges that software engineers (designers, developers) still have to face in their everyday work is the evolution of working database systems. As a step for the solution of this problem in this paper we propose MeDEA, which stands for Metamodel-based Database Evolution Architecture. MeDEA is a generic evolution architecture that allows us to maintain the traceability between the different artifacts involved in any database development process. MeDEA is generic in the sense that it is independent of the particular modeling techniques being used. In order to achieve this, a metamodeling approach has been followed for the development of MeDEA. The other basic characteristic of the architecture is the inclusion of a specific component devoted to storing the translation of conceptual schemas to logical ones. This component, which is one of the most noteworthy contributions of our approach, enables any modification (evolution) realized on a conceptual schema to be traced to the corresponding logical schema, without having to regenerate this schema from scratch, and furthermore to be propagated to the physical and extensional levels.     

城市地理空间数据框架建设的实践与探讨

阐明了城市地理空间数据框架建设的必要性，说明它在城市信息化过程中的作用更大，应用更加广泛，在目前情况下、更易推动地理信息数据共享，并结合西安市的具体实践，探讨了其建设内容、建设过程和更新方法。     

基于VFP的数据库完整性设计

完整性约束是数据模型的重要组成部分，在应用系统开发中数据库完整性的设计十分重要。本文从实体完整性、参照完整性和用户自定义完整性三方面探讨了数据库完整性理论，并通过实例介绍了在VFP6．0中数据库完整性的设计。     

Video-graphic query facility for database retrieval

The goal of this project was to develop a prototype to demonstrate the use of video and graphic techniques applied to the human-machine interface for data retrieval from a typical computerized database. Data is presented to a user via video and graphic means; queries are formulated in one of several graphic formats; control operations are handled through joystick, touch panel, or single-keystroke maneuvers. To accomplish this, we made use of videodisc, interactive computer graphics, and relational database technologies. Still pictures, video segments, and pictures of text are used as visual cues to a user who indicates interest in a data item in a pointing gesture by touching the panel through which the item may be seen. The user may find the actual data item s/he desires, then pose a query for additional information in one of four graphic query formats. A specially designed database was developed to handle the video and graphic data needed for this user facility.     

基于INTERNET的企业数据库同步设计方案

文章基于对企业数据库系统数据复制和数据同步的分析,对数据库的数据同步的概念、结构及设计方法进行了阐述,提出了一种全新的适合中国企业模式的数据库数据复制和数据同步的解决方案,并结合实际的实施案例对数据同步这一重要概念进行了初步的探讨。     

开发MIS系统时各元素名称的命名技巧

本文以FOXPROFORWINDOWS为例，阐述了利用FOXPRO开发较大型MIS系统时，如何为字段、内存变量、数组、数据库文件以及其它文件命名，才能使开发者在开发过程中更加有步骤地完成开发任务，而不致于在大量的名称面前产生混乱，减少开发过程中不必要的错误，少走弯路。     

Using databases in history teaching

Abstract In recent years, considerable interest has been shown in the classroom use of historical databases. Several database programs for microcomputers have become available, and as far as history teaching is concerned, they appear to have been mainly used for the analysis of mid-nineteenth century census schedules. At the same time, it is not clear that the curricular issues concerning the use of these programs has been fully explored. The purpose of this article is to raise these issues and to relate them to the use of several database programs currently used in classroom history teaching.     

Energy use in the rural areas of India: setting up a rural energy data base

Aggregating and forecasting demand are crucial parts of energy planning. While a large number of energy consumption surveys have been conducted in the past in the rural energy sector of India, the lack of sufficient data and its compilation, coupled with doubt about the quality of data, has made the task extremely difficult. This paper summarizes our recent effort to compile, computerize and analyze data from 638 village energy consumption surveys covering over 39,000 households, carried out by different organisations between 1985 and 1989. The details of the level of information provided in the survey reports, area of survey, land use pattern, asset ownership, etc., of the collated studies are presented. Results based on the analysis of the energy consumption data compiled are then discussed. The national average for rural domestic thermal energy consumption (excluding water and space heating) estimated through this work (629 kcal or 2.63 MJ per capita daily) is much similar to the rural domestic thermal energy requirement assumed in most energy planning exercises in India in the past. The useful thermal energy consumption varies from 325 to 1065 kcal/cap/d (1.36-4.46 MJ/cap/d) in the East Coast Plain and Hills and the Eastern Himalayan Regions, respectively. Reconfirming the predominance of firewood, the data reveals that the contribution of firewood to the domestic thermal energy consumption has remained at about 58% over the last three decades; dungcake and agricultural residues contribute almost equally in the remaining share. At the national level, our estimates indicate that at least 180 million tonnes of firewood, 40 million tonnes of dungcakes and 30 million tonnes of agricultural residues were consumed in the rural sector for meeting the domestic thermal energy requirement in 1991. The paper also compares the estimates with those based on other surveys in India.     

Converting SQL queries into relational algebra

We present an algorithm for converting a semantically meaningful SQL query into an equivalent algebraic expression. The relational algebra we employ consists of the following operators: union, intersection, difference, Cartesian product, selection, and projection. The SQL queries we consider can have an arbitrary level of nesting but are restricted in three ways. We assume that they do not contain an ORDER BY or a GROUP BY clause, all SELECTs are in fact SELECT DISTINCTs, and that no aggregate functions are used. The first two assumptions are made in order to remain faithful to the definition of a relation as a set of rows. The last assumption is needed since there is no standard for incorporating aggregate functions into a relational algebra. The research results in this paper will be useful in implementing an SQL user interface for database management systems that internally employ relational algebra. They can also be used in optimizing the evaluation of SQL queries.