ROLE OF DATABASE ADMINISTRATOR (DBA)
Database Administrator (DBA) is the person responsible for Supervising the database and the use of DBMS in an organization. DBA has the following responsibilities.
• Designing the database and enforcing the operational policies and procedures for its usage
• Planning Security measures and backup of database
• Controlling privileges and permissions of database users
• Allocating passwords to users
• Planning recovery procedures if hardware or software failure occurs and ensuring that no
data is lost.
• Providing training to new employees about using the database
A database model is the theoretical foundation of a database and determines in which manner data can be stored, organized and manipulated. It defines a way of structuring data. There are five types of database models.
Hierarchical Database Model:-
In a hierarchical model, data is organized into a tree-like structure. It is a logical Construct with owner and subordinate relationship. Data elements in a subordinate relationship are called members and those having subordinates are called Owners. In a hierarchical Structure Subordinates Can have only a single Owner and there is only one data element that has no Owner. This structure is very suitable in describing many relationships in real World. Some examples of hierarchical model are table of Contents, departments of an organization and types of memories.
Network Database Model:-
A network model is a logical structure in which some of the data elements can have more than One Owner data element. A network is a more complex structure than a hierarchical model. A hierarchical model can be thought of as a network with Some discipline imposed on it. An application with which Crew members, aircraft, routes and Schedules are related is by its nature a network model.
Relational Database Model:-
In a relational database model, data is held in tables and the tables are linked by means of common fields. The relation in a relational database refers to the Various tables in the database which are linked with each other. A table in database consists of rows and columns.One row of table holds one record.Each column in the table holds one field or attributes.
The relational database model is used to make database management systems more independent of any particular application. It is the most popular database model used in business applications.
Object-Oriented Database Model:-
Object-oriented databases are also called Object Database Management Systems (ODBMS). Object databases store objects rather than data such as integers, real numbers and strings. Objects are used in object oriented programming languages Such as C++ and Java.
Real World objects have two characteristics, that is, state and behaviour. For example, the object radio has four states and five behaviours as shown in Fig. 7.4. An object stores its states in variables and exposes its behaviour through functions in programming languages.
Object Relational Database Model:-
An Object Relational Database (ORD) is a database management system similar to relational database, but with an object-oriented database. In object relational database, the approach is essentially that of relational database. The data resides in the database and is manipulated Collectively with queries in a query language.