Relational Model in DBMS : RDBMS Concepts

RDBMS Concepts -

-> Relational Database management System(RDBMS) is a database management system based on the relational model introduced by E.F Codd. In relational model, data is stored in relations(tables) and is represented in form of tuples(rows).



-> RDBMS is used to manage Relational database. Relational database is a collection of organized set of tables related to each other, and from which data can be accessed easily. Relational Database is the most commonly used database these days.


-> A relational database has following major components:-

1. Table or relations
2. Record or Tuple or rows
3. Field or Column name or Attribute
4. Domain
5. Instance
6. Schema

7. Keys



1. Table -  A table is a collection of data represented in rows and columns. Each table has a name in database.

-> A table is also considered as a convenient representation of relations. But a table can have duplicate row of data while a true relation cannot have duplicate data. Table is the most simplest form of data storage. Here example of an Employee table.

ID	Name	Age	Salary
1	Amit	20	18000
2	Akshay	28	15000
3	Rajesh	20	16000
4	Rikesh	40	17000

2. Record or Tuple -    Each row of a table is known as record. It is also known as tuple or rows. A tuple in a table represents a set of related data. For example, the above Employee table has 4 tuples/records/rows.

For example, the following row is a record that we have taken from the above table.

3

Rajesh

20

16000

3. Field or Column name or Attribute -   A table contains several records(row), each record can be broken down into several smaller parts of data known as Attributes. 

The above Employee table consist of four attributes, ID, Name, Age and Salary.

4. Attribute Domain -  When an attribute is defined in a relation(table), it is defined to hold only a certain type of values, which is known as Attribute Domain.

-> Every attribute has some pre-defined value scope, known as attribute domain.

-> An attribute cannot accept values that are outside of their domains. For example, In the above table “STUDENT”, the Student_Id field has integer domain so that field cannot accept values that are not integers.


5. Instance and Schema -  I have already covered instance and schema in a separate tutorial, you can refer the tutorial; click here 

6. Keys -  I have covered the keys in detail in separate tutorials.  You can refer the keys tutorial; click here 





NULL Values

The NULL value of the table specifies that the field has been left blank during record creation. It is totally different from the value filled with zero or a field that contains space.


Data Integrity

There are the following categories of data integrity exist with each RDBMS:


Entity integrity: It specifies that there should be no duplicate rows in a table.


Domain integrity: It enforces valid entries for a given column by restricting the type, the format, or the range of values.



Referential integrity: It specifies that rows cannot be deleted, which are used by other records.

User-defined integrity: It enforces some specific business rules that are defined by users. These rules are different from entity, domain or referential integrity