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Attributes

RGPV: DBMS: Unit 2
 

ATTRIBUTE

 

In general, an attribute is a characteristic.

It is the name of the column.

An attribute gives the characteristics of the entity.

In a database management system (DBMS), an attribute refers to a database component, such a table.

It also may refer to a database field.

Attributes describe the instances in the row of a database.

 

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 –

1)      Single Values 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.

 

2)      Simple/Atomic Attributes:

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

 

3)      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.

 

4)      Compound/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.

 

5)      Derived Attribute:

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

 

6)      Key Attributes :

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.

 

7)      Required Attributes:

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.

 

8)      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.

 

9)      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.

 

10)  Optional/Null Value Attributes:

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.

 

11)  Stored Attribute:

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

 

 

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