Oracle OCA course Beginner level by Winavit Technologies Pvt Ltd

Database Management System (DBMS)

A database management system (DBMS) is software that controls the storage, organization, and retrieval of data. Typically, a DBMS has the following elements:

Kernel code

This code manages memory and storage for the DBMS.

Repository of metadata

This repository is usually called a data dictionary.

Query language

This language enables applications to access the data.

A database application is a software program that interacts with a database to access and manipulate data.

The first generation of database management systems included the following types:

Hierarchical

A hierarchical database organizes data in a tree structure. Each parent record has one or more child records, similar to the structure of a file system.

Network

A network database is similar to a hierarchical database, except records have a many-to-many rather than a one-to-many relationship.

The preceding database management systems stored data in rigid, predetermined relationships. Because no data definition language existed, changing the structure of the data was difficult. Also, these systems lacked a simple query language, which hindered application development.
Relational Model

In his seminal 1970 paper "A Relational Model of Data for Large Shared Data Banks," E. F. Codd defined a relational model based on mathematical set theory. Today, the most widely accepted database model is the relational model.

A relational database is a database that conforms to the relational model. The relational model has the following major aspects:

Structures

Well-defined objects store or access the data of a database.

Operations

Clearly defined actions enable applications to manipulate the data and structures of a database.

Integrity rules

Integrity rules govern operations on the data and structures of a database.