E-R and EER Models: Types of Attributes

Attributes can be characterized by the following Three major types :

1. Simple and Composite Attributes

Simple Attributes  are those  which cannot  be  divided into  subparts.

Ex. Age of student        

Composite Attributes  are those  which can  be  divided into  subparts.

Ex. Name of a student can be divided into First Name, Middle Name, and Last Name.

2. Single Valued and Multi-valued Attributes

Single Valued Attribute : An attribute having only single value for a particular entity is known as single value attribute.

Ex. Age of student.

Multi-Valued Attributes : An attribute having more than one possible value for a particular entity is known as multi-valued attribute.

Ex. Phone  number  of a  student. A student may  have  more than  one  phone.

3. Derived Attributes and Stored Attributes

Derived Attributes : An attribute that can be derived from other known attributes is known as derived attribute.

Ex. Age of employees can be derived if you know date of birth and system date.

Age = System date – Date of birth

Stored Attributes : An attribute which cannot be derived by other known attributes is known as stored  attribute.

Ex. Date of birth of any employee.

NULL Value : Null stands for nothing. An attribute have a null value if either the value of that attribute is not known or the value is not applicable.

Caution : NULL is not equal to Zero (0). But you can say that NULL is blank as shown in Figure  2.2.

Source: Gupta Satinder Bal, Mittal Aditya (2017), Introduction to Database Management System, 2nd Edition-University Science Press (2017)

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