Class 11th Informatics Practices Notes: Exam Preparation Made Easy Unit-3

 Unit 3: Database concepts and the Structured Query Language 

*Introduction to Database Concepts*

- A database is a collection of organized data that can be easily accessed, managed, and updated.

- Need for databases:

    - To store and manage large amounts of data

    - To provide quick access to data

    - To ensure data consistency and accuracy

    - To provide data security

*Database Management System (DBMS)*

- A DBMS is a software system that allows you to define, create, maintain, and manipulate databases.

- Functions of DBMS:

    - Data definition: defining the structure of the database

    - Data manipulation: inserting, updating, and deleting data

    - Data retrieval: querying and retrieving data

    - Data security: controlling access to data

    - Data backup and recovery: ensuring data safety

*Key Features of DBMS*

- Data independence: separating data from applications

- Data redundancy control: minimizing data duplication

- Data integrity: ensuring data accuracy and consistency

- Data security: controlling access to data

- Backup and recovery: ensuring data safety

*Types of DBMS*

- Hierarchical DBMS

- Network DBMS

- Relational DBMS (RDBMS)

- Object-oriented DBMS (OODBMS)

*Relational Database Management System (RDBMS)*

- Based on relational model

- Uses tables to store data

- Uses SQL (Structured Query Language) for data manipulation and retrieval. 

Here are some notes on the Relational Data Model:

*Domain*:

- A set of allowed values for an attribute

- Defines the data type and range of values for an attribute

- Example: Age domain: 0-120

*Tuple*:

- A single row in a relation

- Represents a single record or entry

- Example: (John, 25, New York) is a tuple in a relation

*Relation*:

- A table with rows and columns

- Represents a collection of tuples

- Example: Employee relation: | Name | Age | City |

*Candidate Key*:

- A minimal set of attributes that uniquely identify each tuple

- Can be used as a primary key

- Example: Employee ID, Name, and Age can be candidate keys

*Primary Key*:

- A selected candidate key that uniquely identifies each tuple

- Used to reference tuples in other relations

- Example: Employee ID is the primary key in the Employee relation

*Alternate Key*:

- A candidate key that is not selected as the primary key

- Can be used as a secondary identifier

- Example: Name and Age can be alternate keys in the Employee relation

Additional notes:

- A relation can have multiple candidate keys, but only one primary key.

- A primary key is used to enforce data integrity and prevent duplicate tuples.

- Alternate keys can be used for querying and indexing purposes.

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