(Continued from previous part...)

Database Administrator:

A database analyst is also responsible for the logical and physical design of databases.


Duties
The duties of a database administrator at a particular site vary, depending on the policies in place and the database management system’s (DBMS’s) capabilities for carrying them out. They nearly always include disaster recovery (backups and testing of backups), performance analysis, and some database design or assistance thereof.

Definition of Database
Before going on, we need to briefly define and describe “database.” A database is a collection of related information, accessed and managed by its DBMS. After experimenting with hierarchical and networked DBMSs during the 1970’s, the IT industry became dominated by relational DBMSs such as Oracle Server.
A relational DBMS manages information about types of real-world things (entities) in the form of tables that represent the entities. A table is like a spreadsheet; each row represents a particular entity (instance), and each column represents a type of information about the entity (domain). Sometimes entities are made up of smaller related entities, such as orders and order lines; and so one of the challenges of a multi-user DBMS is provide data about related entities from the standpoint of an instant of logical consistency.
Properly managed relational databases minimize the need for application programs to contain information about the physical storage of the data they access. To maximize the isolation of programs from data structures, relational DBMSs restrict data access to the messaging protocol SQL, a nonprocedural language that limits the programmer to specifying desired results. This message-based interface was a building block for the decentralization of computer hardware, because a program and data structure with such a minimal point of contact become feasible to reside on separate computers.

Recoverability
Recoverability means that, if a data entry error, program bug or hardware failure occurs, the DBA can bring the database backward in time to its state at an instant of logical consistency before the damage was done. Recoverability activities include making database backups and storing them in ways that minimize the risk that they will be damaged or lost, such as placing multiple copies on removable media and storing them outside the affected area of an anticipated disaster. Recoverability is the DBA’s most important concern.
Recoverability, also sometimes called "disaster recovery," takes two primary forms. First the backup, then recovery tests.
The backup of the database consists of data with timestamps combined with database logs to change the data to be consistent to a particular moment in time. It is possible to make a backup of the database containing only data without timestamps or logs, but the DBA must take the database offline to do such a backup.
The recovery tests of the database consist of restoring the data, then applying logs against that data to bring the database backup to consistency at a particular point in time up to the last transaction in the logs. Alternatively, an offline database backup can be restored simply by placing the data in-place on another copy of the database.
If a DBA (or any administrator) attempts to implement a recoverability plan without the recovery tests, there is no guarantee that the backups are at all valid. In practice, in all but the most mature RDBMS packages, backups rarely are valid without extensive testing to be sure that no bugs or human error have corrupted the backups.

Integrity
Integrity means that the database, or the programs that create its content, embody means of preventing users who provide data from breaking the system’s business rules. For example, a retailer may have a business rule that only individual customers can place orders; and so every order must identify one and only one customer. Oracle Server and other relational DBMSs enforce this type of business rule with constraints, which are configurable implicit queries. To continue the example, in the process of inserting a new order the database may query its customer table to make sure that the customer identified by the order exists.

(Continued on next part...)