what is an attribute ? what are the types of attributes?

What is an attribute?

Attribute is a descriptive property of an entity. or It describe the entity. for example if an apple is an entity its attribute will be its color, shape, size.

There are many types of an attribute.

• Simple attribute
• Composite/compound attribute
• Single value attribute
• Multivalued attribute
• Null attribute
• Derived attribute

Simple attribute : An attribute whose value can't be subdivided further. example :roll no.  ,branch.

Compound attribute : An attribute whose value can be further subdivided into another attributes. example: name.

Single value attribute :  An attribute which take only one value. example :Religion ,Nationality ,Age .

Multivalued attribute :It can take more than one value at a certain instant of time. example :email id , address.

Derived attribute : An attribute whose value can be derived from other attribute. example : From date of birth we can know the age.

NULL attribute : An attribute which take NULL value. NULL value indicates that the value for attribute is currently not available .  at that particular time you have no value. NULL is not zero. Primary key attribute can't contain NULL value.