The Computer Revolution/Databases/RDBMS

Relational Database Management Systems: ORACLE DATABASE 11g

ORACLE

A database management system includes adding new data, updating or altering data on the database. What about Relational Database Management Systems or known as RDBMS?

An RDBMS is a Database Management System that is based on a relational model. In this data model, data is stored in the form of tables. And again, a data model is a way of storing and retrieving data. A good example of an RDBMS is Oracle.

Oracle database is an object RDBMS used as a platform by many mainstream companies to keep track of large amount of data and databases. The reason is for it being the best DBMS tool is that it can backup and restore data efficiently, manage data integrity, data security, tuning and performance of databases and other features as well. Within Oracle, there is a program called SQLPLUS which is used to create tables, input information and alter data in those tables. SQLPLUS is the most important tool in Oracle. It is also used for mounting databases, creating users, granting them different permissions and roles. The different versions of Oracle are 8i, 9i, 10g, 11i and 11g A database consists of three main things:

     •  Storage
     •	Memory Structures
     •	Processes (Instances)

Oracle has physical and logical form of storage structures. It stores data in the form of logical Table spaces, which is a collection of physical data files stored in the form of physical oracle Data Blocks. An Oracle data block is the lowest allocation unit of data. Now what exactly is a table space?

     •  A database is made up of one or more Table Spaces.
     •	Table Spaces allow you to logically separate the data.
     •	Table Spaces are created for better management of the data and simplifying administrative tasks
     •	Table Spaces have names. For example: “Users”
     •	A database configuration assistant (DBCA) creates the default Table Spaces which are: SYSTEM, SYSAUX, USERS, TEMP AND UNDOTBS1

When a Table Space is assigned to a user, all the schema information related to that user, is stored in that particular Table Space.

An Oracle Instance consists of two main memory structures. The System Global Area known as the “SGA” and the Program Global Area (PGA). It also consists of several other background processes that are responsible for various other tasks. These memory structures and background processes make up an Oracle instance. A database cannot be mounted if the instance isn't started. The SGA and PGA play an important role in database tuning.

One of the crucial things in maintaining a database is back-up and recovery. In case a database crashes, Oracle has an inbuilt tool called the RMAN, Recovery Manager. This tool runs very efficiently and users can back up and restore a database to an earlier stage, manually or program it to take automatic backups and send a log report via email. This makes Oracle Databases an excellent relational database management system.

Reference: Bob Bryla and Kevin Loney. Oracle Database 11g DBA Handbook: Oracle Press, 2007