Derived attribute in DBMS

Derived Attribute in DBMS

On this page, we will learn about Derived Attribute in DBMS.

derived

A derived attribute as the name suggests is the one that can be
derived or calculated with the help of other attributes present themselves.

For example – The age of the student can be calculated from
‘date of the birth present as an attribute.

Representation: Horizontal Dashed Oval

Derived attribute in DBMS

Definition of a derived attribute

  • A derived attribute data  is derived (copied)  from the attribute of  another table
  • The derived attribute value is always dynamic.

Example of a derived attribute 

If you need to copy the age data from another table to the student table then and age attribute will become derived attribute in the student table

Representation of derived attribute

In the ER diagram, the derived attribute is represented by a dashed oval with a name inside the dashed oval 

Derived vs Stored Attribute

Stored AttributeDerived Attribute
It must be explicitly stored in databaseIt may not be explicitly stored as it can be derived from another attribute
It is not possible to determine stored attribute value from another attributeIt is possible to determine derived attribute value from another attribute
Stored attribute will be fixed.Derived attribute will be variable in nature
Represented by an ovalRepresented by a dotted oval
Since, value is direct it saves CPU timeCPU time is consumed in derivation from another attribute
It saves data access time if it is not stored in the Relational table, then the data access time is longer
Requires constant maintenance. To keep the most updated value. Also in order to make sure that its parallel derived attribute has latest valueDerived attribute may not need maintenance. However, its parallel stored attribute may need it.
Does not add coding complexity to queriesAdds coding complexity to queries, if not stored in the Relational table
Readily available value data value is not readily available, if not stored in the Relational table

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