Database

The Worlds of Database Systems

Databases today are necessary to each business. They are used to maintain internal records, to present data to customers and clients on the World-Wide-Web, and to support many other commercial processes.

The Evolution of Database Systems

What is a database? In real meaning a database is nothing more than gathering of information that exists over a long phase of time, often many years.

Early Database Management Systems

The first commercial database management systems appeared in the late 1960's. These systems evolved from file systems, which offer some of item (3) above; file systems accumulate data over a long phase of time, and they allow the storage of huge amounts of data.

Corporate Records

Many early applications concerned corporate records, such as a record of each sale, information about accounts payable and receivable, or information about employees their names, addresses, salary, benefit options, tax status, and so on.

Smaller and Smaller Systems

In the beginning, DBMS's were large, expensive software systems running on large computers. The size was compulsory, because to store a gigabyte of data required a large computer system.

Data-Definition Language Commands

The second type of command is the simpler to process, and we show its trail beginning at the upper right side of Figure. For example, the database administrator, or DBA, for a university registrar's database

Storage and Buffer Management

The data of a database generally exists in secondary storage; in today's computer systems secondary storage" generally means magnetic disk. However, to carry out any useful operation on data,

Information Integration Overview

Much of the recent development of database systems has been toward capabilities that allow different data sources, which may be databases and / or information resources that are not managed by a DBMS

Choosing the Right Relationships

Entity sets can be joined in different ways by relationships. However, adding to our design every possible relationship is not often a good idea. First, it can lead to redundancy, where

Relation Instances

A relation about movies is not stationary; rather, relations change over time. We expect that these changes include the tuples of the relation, such as insertion of new tuples as movies

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