1.1. An Overview of Databases and Instances

Although the terms "database" and "instance" are often used interchangeably, they are quite different. They are very distinct entities in an Oracle datacenter, as you shall see in the following sections.

1.1.1. Databases

A database is a collection of data on disk in one or more files on a database server that collects and maintains related information. The database consists of various physical and logical structures, the table being the most important logical structure in the database. A table consists of rows and columns containing related data. At a minimum, a database must have at least tables to store useful information. Figure 1-1 shows a sample table containing four rows and three columns. The data in each row of the table is related: Each row contains information about a particular employee in the company.