文档介绍：(2009 届毕业设计) 外文翻译原文及译文学院(部): 计算机与通信学院专业: 计算机科学与技术学生姓名: 许淦班级: 计 052 学号 0540810215 指导教师姓名: 李建设职称副教授 2009 年4月 The Semantic Web: An Overview Data Independence An important point about database systems is that the database should exist independently of any of the specific applications. Traditional data processing applications are data dependent. COBOL programs contain file descriptions and record descriptions that carefully describe the format and characteristics of the data. Users should be able to change the structure of the database without affecting the applications that use it. For example, suppose that the requirements of your applications change. A simple example would be expanding ZIP codes from five digits to nine digits. On a traditional approach using COBOL programs each individual COBOL application program that used that particular field would have tobe changed, piled, and retested. The programs would be unable to recognize or access a file that had been changed and contained a new data description; this, in turn, might cause disruption in processing unless the change were carefully planned. Most database programs provide the ability to change the database structure by simply changing the ZIP code field and the data-entry form. In this case, data independence allows for minimal disruption of current and existing applications. Users can continue to work and can even ignore the nine-digit code if they choose. Eventually, the file will be converted to the new nine-digit ZIP code, but the ease with which the changeover takes place emphasizes the importance of data independence. Data Integrity Data integrity refers to the accuracy, correctness, or validity of the data in the database. Ina database system, data integrity means safeguarding the data against invalid alteration or destruction arise. The first has todo with many users accessing the database concurrently. For example, if thousands of travel agents and airline reservation clerks are accessing the databas