文档介绍：Database Systems
Fundamental Concepts of Database
Database and database technology are having a major impact on the grlexity. For example, the list of names and addresses referred to earlier may have only a couple of hundred records in it, each with a simple structure. On the other hand, the card catalog of a large library may contain half a million cards stored under different categories-by primary author
's last name, by subject, by book title, and the like-with each category organized in alphabetic order. A database of even greater size and complexity may be that maintained by the Internal Revenue Service to keep track of the tax forms filed by taxpayers of the United States. If we assume that there are 100million taxpayers and each taxpayer files an average of five forms with approximately 200 characters of information per form, we would get a database of 100*(10 6)*200*5 characters(bytes) of information. Assuming the IRS keeps the past three returns for each taxpayer in addition to the current return, we would get a database of 4*(1011) bytes. This huge amount of information must somehow be organized and managed so that users can search for, retrieve, and update the data as needed.
A database may be generated and maintained manually or by machine. Of course, in this we are mainly interested in computerized database. The library card catalog is an example of a database