Database – What is Database Management System & Their Components



  • It is a collection of programs that enables users to Store, Modify, and Retrieve information from a database
  • It provides the interface between the user and the database.

Primary Key:

  • The field which has Primary Key can’t be null and duplicate.
  • If primary key is made of only one field, it is called “Simple key”
  • If primary key is made of a group of two or more fields, it is called “Composite key”.

Data Type:

  • Text (Used to store alphabets, digits and special characters. It can store up to 255 characters).
  • Memo (Used to store a large amount of text data).
  • Number (Used to store numeric data)
  • Date/Time (Used to store Date and Time).
  • Currency (Used to store Currency amounts).
  • Auto Number (Used to generate a serial number).
  • Yes/No (This field contain either Yes or No).

ENTITY-RELATIONSHIP MODEL:

  • Also called E-R Model.
  • It is the graphical representation of the database.
  • In E-R Model Entities and their relationship described.

Entity:

  • An entity is a person, place, event or a concept in the real world.
  • Each entity has a set of attributes or properties.
  • For example, in a school, each student is an entity. This entity has the attributes of Name, Roll No, Class, Date of Birth, Phone No etc.

Relationship:

  • Linking of records of one table with the records of another tables is called “Relationship”.
  • The field(s) in both tables usually have the same name, data type and size
  • Three types of relationships are
  1. One-to-One Relationship
  1. One-to-Many Relationship
  1. Many-to-Many Relationship

One-to-One Relationship:

  • Relationship between two sets of entities A and B is one-to-one when

o For each entity in A, there is only one related entity in B,and

o  For each entity in B, there is only one related entity in A.

  • For example, countries and their capitals.

One-to-Many Relationship:

Relationship between two sets of entities A and B is one-to-many when

o For each entity in A, there can be one or more than one related entities in B, and

o  For each entity in B, there is only one related entity in A.

  • For example, a student can have more than one phone numbers but phone number could be assigned to only one student.

Many-to-Many Relationship:

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