Before jumping to RDBMS, we recommend you to read Introduction to Database Management Systems

Relation Database Management System (RDBMS) works on the mathematical theory of relations. Relational model was first formulated and proposed in 1969 by Edgar F. Codd. A table is called a relation in RDBMS.

**Table**

A table is a collection of rows (or tuples) and columns.

- The number of columns in a table is called its
**degree**.
- The number of rows in a table is called the
**cardinality** of the table.

- The set of values of one column in a table is called a domain.

**Domain**

A domain is a set of all possible values for a column or a table.

For example, suppose we have a column called course_name in a Course table. Then, the set of all possible course names is the domain.

**Examples of domains**

**Domain** |
**Importance** |

India_Aadhar_UID |
Set of valid aadhar numbers in India |

Student_RollNumber |
Set of valid roll numbers of students in a college |

Name |
Set of all possible names of the person |

You can see that Student roll number and name have completely different domains. Data from one domain cannot be compared with other domain.

**Some of the characteristics of domain are:**

- Name
- Data type
- Format
- Unit of measurement
- Range or list of allowed values

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Read next: RDBMS – Database Integrity ››

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