Database for beginners

A Database Management System (DBMS) is a software used to store data and manage data. A DBMS store data in databases and uses data models to describe the various ways of organizing the data.

A Database is the collection of logically related information. Database Management is the task of maintaining a database so that information is readily available. The software required to perform the task of database management is called a Database Management System. DBMS are designed to maintain a large volume of data.

Data Models

Data model is a description of the organization of data in the database. Data models also describe the relationships among data and any constraints that have to be defined on the data. Data models can broadly be classified into two categories:

Object Based Logical Model

Focuses on describing the data, the relationship among the data, and any constraints defined

There is various Object Based Logical Models and mostly used model is ER model (Entity Relationship Model). ER model is based on real world perception the comprises a collection of objects or entities and the relationship among these.

Entities

We define an entity as a thing, which can easily identify. An entity is any object, place, person, or activity about which data is recorded. Following are some examples of entities
Student
Course
Grade

Relationships
We define the relationship as an association among entities. For example, there is a relationship between student and instructors. This relationship represents the fact that an instructor teaches several students and a student is taught by several instructors. There are three types of relationships:

One-to-one (For example One Department Headed by One department head)

database-relationship-onetoone
database-relationship-onetoone

One-to-Many (For example: One Student related to many subjects)

database-relationship-onetomany
database-relationship-onetomany

May-to-one (For Example: Many employees belong to one department)

database-relationship-manytoone
database-relationship-manytoone

Many-to-Many (For example: Many Students related to many Subjects)

database-relationship-manytomany
database-relationship-manytomany

Record based Logical Model

Focuses on describing the data structure and the access techniques in a Database Management System.

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One-to-one (For example: One Department Headed by One department head)instructors. Thithe fact that an instructor teaches several students and a student is taughtere are three types of relationships:

One-to-one (For example: One Department Headed by One department head)

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