Attributes in ER Model

Attributes are the properties of entity in an entity set.
There are various types of attributes in ER Model.

Types Of Attributes

Let explain the Various types of attributes one by one.

1. Simple Vs. Composite Attributes

Simple Attribute	Composite Attribute
The attribute which cannot further split into its components is a simple attribute.	An attribute which can split into components is known as composite attribute.
Example: The roll number of a student, the id number of an employee etc.	Example: Name of the student can split into first, middle and last name.

2. Complex Attributes

If a composite attributes further split into its components then it will be a complex attributes. In the following diagram the street is a complex attribute

3. Single-Valued Vs. Multi-Valued Attributes

Single-Valued Attribute	Multi-Valued Attribute
The attribute which has a single value for each entity instance is known as single-valued attribute. There is no alternative of this value.	The attribute which takes up more than one value for each entity instance is known as multi valued attribute.
Example: The Registration No, RollNo, DOB, Gender of a student will always be a unique.	Example: Phone number of any person can be a mobile and Landline number.

Note: Multi-valued attribute represents through double Circles.

4. Stored Vs. Derived Attributes

Stored Attribute	Derived Attribute
Those attribute which cannot derive from other attributes.	An attribute which is derived from other attributes is a derived attribute.
Example: DOB cannot derive in the same way CNIC etc.	Example: Age of student can be derived from DOB.

5. Key Vs. Non-Key Attributes

Key Attribute	Non-Key Attribute
It represents the primary key which is used to uniquely identify the instance (entire row) of entity.	Those attributes which cannot use as primary key are known as non-key attributes.
Example: Roll_No, Student_ID or Student_RegNo etc.	Example: Student name, address etc.

Note: This attribute represented with a circle containing and underline as well.

6. Required Vs. Optional Attributes

It is mostly use in filling the application forms. Sometimes Phone number is optional and Name is mandatory.

Required Attribute	Optional Attribute
Those attributes which are mandatory are called required attributes	Those attributes which are not mandatory are called Optional attributes