Introduction to Database Concept Class 12 Notes
Database Management System:
A Database Management System (DBMS) is a software that can be used to create and manage databases. DBMS allows users to create a database, store, manage, update/modify and retrieve data from that database by users or application programs. Some examples of DBMS are MySQL, Oracle, PostgreSQL, SQL Server, Microsoft Access, MongoDB.
Key Concepts in DBMS:
1. Database Schema:
Database Schema is the design of a database. It is the skeleton of the database that represents the structure (table names and their fields/columns), the type of data each column can hold, constraints on the data to be stored (if any), and the relationships among the tables. Database Schema is also called as the visual or logical architecture as it tells how the data are organized in a database
2. Data Constraint:
Constraints are the conditions that are put on columns for ensuring accuracy and reliability of data being stored in a table. Some constraints are NOT NULL, UNIQUE, PRIMARY KEY etc
3. Meta–Data or Data Dictionary:
The database schema along with various constraints on the data is stored by DBMS in a database catalog or dictionary, called meta-data. A meta-data is data about the data.
4. Database Instance:
After creating a database it is empty, that is without data. Further it is possible add, remove or modify data in database. The data present in database at any state is known as Database Instance
A query is a request to a database for obtaining information in a desired way. Query can be made to get data from one table or from a combination of tables.
6. Data Manipulation:
In a database, Inserting or Deleting or Updating of data is referred as Data Manipulation.
7. Database Engine:
It is the underlying component or set of programs used by a DBMS to create database and handle various queries for data retrieval and manipulation.
Database Concept Class 12 Notes
Relational Data Model:
A Data Model gives the way of representing data. Different data models available are Object–Oriented Data Model, Entity–Relationship Data Model, Document Model, Hierarchical Model, Relational Data Model etc. If the data has been represented in form of Relations (Tables) then such a model is called as Relational Data Model.
1. Relation / Table:
A two dimensional representation of data arranged in form of rows and columns is called a Relation or Table. In the above example, the name of the relation is STUDENT
The column names or characteristics of the table are known as Attributes or Fields.
The horizontal subset of a table is called as Tuple or Row or Record. In the above example, there are 6 tuples.
It refers to the set of values that can be provided to a column.
The number of attributes in a table is called as Degree of the table.
The number of tuples in a table is called as Cardinality of the table.
Database Concept Class 12 Notes
Keys in a Relational Database:
The tuples within a relation must be distinct. It means no two tuples in a table should have same value for all attributes. Relational data model imposes some restrictions or constraints on the values of the attributes and how the contents of one relation be referred through another relation. A few keys used in Relational Database are as follows
1. Candidate Key:
A Candidate key is an attribute or combination of attributes that can uniquely identify a row. A table may have more than one candidate key.
2. Primary Key:
A Primary Key is an attribute or combination of attributes that uniquely identifies a row and shows two characteristics called UNIQUE and NOT NULL. A Primary Key will be one from the available candidate keys. A table may consist of only one primary key.
3. Alternate Key:
All the Candidate keys except Primary Key are called as Alternate Keys.
4. Composite Primary Key:
If a Primary Key is having more than one attributes then such a Primary Key is called as Composite Primary Key.
5. Foreign Key:
A Foreign key is used to link two tables with primary key and foreign key relationship that enforces referential integrity. Consider the below example