Notes on DBMS: Attributes and Its types

Attribute : It is the name of the column. An attribute gives the characteristics of the entity. For example, A customer of bank may be described by : name, address, customer ID number. It is also called as data element, data field, a field, a data item, or an elementary item.

Type of Attributes in DBMS –

Single valued Attributes : An attribute, that has a single value for a particular entity is known as single valued attributes. For example, age of a employee entity.

Multi valued Attributes : An attributes that may have multiple values for the same entity is known as multi valued attributes. For example colors of a car entity.

Compound Attribute/Composite Attribute : Attribute can be subdivided into two or more other Attribute. For Example, Name can be divided into First name, Middle name and Last name.

Simple Attributes/Atomic Attributes : The attributes which cannot be divided into smaller subparts are called simple or atomic attributes. For example, age of employee entity

Stored Attribute : An attribute, which cannot be derived from other attribute, is known as stored attribute. For example, BirthDate of employee.

Derived Attribute : Attributes derived from other stored attribute. For example age from Date of Birth and Today’s date.

An attribute can be derived from a single attribute. Example age from DOB and current date.
An attribute can be derived from multiple attribute.
An entity can be derived from a separate table. Example,

RNO Name DeptNO

1 A 1

2 B 1

3 C 2

4 D 3

5 E 1

⇒

DNO Dname

1 CSE

2 IT

3 ECE

Complex Attributes : If an attribute fr an entity, is built using composite and multivalued attributes, then these attributes are called complex attributes. For example, a person can have more than one residence and each residence can have multiple phones, an addressphone for a person entity can be specified as –

{Addressphone (phone {(Area Code, Phone Number)}, Address(Sector Address (Sector Number,House Number), City, State, Pin))}

Here {} are used to enclose multivalued attributes and () are used to enclose composite attributes with comma separating individual attributes./

Key Attribute : represents primary key. (main characteristics of an entity). It is an attribute, that has distinct value for each entity/element in an entity set. For example, Roll number in a Student Entity Type.

Non Key Attributes : These are attributes other than candidate key attributes in a table. For example Firstname is a non key attribute as it does not represent the main characteristics of the entity.

Required Attribute : A required attribute is an attribute that must have a data value.These attributes are required because they describe what is important in the entity. For example, In a STUDENT entity, firstname and lastname is a required attribute.

Optional Attribute/Null Value Attribute – An optional attribute may not have a value in it and can be left blank. For example, In a STUDENT entity, Middlename or email address is an optional attribute. as some students may not have middlename or email address.