Derived attribute in ER Model

Question

Can anybody please explain me the concept of Derived attribute (in the following special case) in ER Model??

Query:Can a derived attribute be derived from Multiple entities? If it can be derivable from multiple entities then how to represent such derived attributes in ER Diagram?

Thanks in Advance!! :)-

Comments

In the very basic sense the derived attributes are those which can be derived from already stored attributes, like age from date of birth, but i guess you already know that.

But to think in more practical sense, let assume bank has an application which decides weather someone gets extended loan or not.

Basic rules :- 

• customer can pay any amount when he has(say, in interval of 60 day).
• and can borrow any amount he needs(depending upon what his history of repaying the debt).
• and let there is one column in the customer details table namely reputation.

now let customer demands for some money to borrow, then the application program will use the reputation value to derive the maximum amount(using some formula which takes initial loan amount and other things into consideration) which can be lend to that particular customer and if customer demand is more than that then, the request will be rejected or an email will be sent to customer, whatever else it will be granted.

Answer 1

Yes it is possible.

For eg. Total Salary in Employee can be derived from basic pay,hra,allowances.

The representation remains same as that of the simple derived attribute.

CORRECT ME IF I AM WRONG.

Comments

Derived attribute : the attribute which is derived from stored attributes is called derived attributes

Ex. Age is derived from date of birth.

Derived attributes are represented in dotted lines.

Answer 2

Derived Attribute: It is an attribute whose value is derived from other attributes.

It is described using by dotted oval