Types Of Attributes
There are several types of attributes in E-R model as given below,
- Simple and composite attributes
The attributes which cannot be divided further is called simple or atomic attributes.The attributes which can be divided into smaller subparts with independent meanings is called composite attribute.
For example, In employee entity, the attribute emp_no is a simple attribute. The emp_name can be called a composite attribute as name can be divided into first name, middle name and last name.
- Single valued and multivalued attributes
The attributes which have a single value for a given entity are said to be single valued attributes. For instance, the employee number attribute refers to only one employee number.
The attributes which have multiple values for a given entity, this type of attributes are called multivalued attributes. For example, an employee can have more than one phone number, therefore phone number is a multivalued attribute.
- Derived attributes:
The value of an attribute can be derived from the other values of other related attributes. For example, the attribute date_of_birth and age are related attributes. Age is a derived attribute which can be calculated using date_of_birth and need not be a part of schema. And date_of_birth attribute is called a stored attribute.