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Apologies if this is a trivial question, I recently started studying about E.R. Model. Let me try to clarify my doubt using an example. Consider the two entities,Customer and Loan in a relationship such that;

Customer (Strong Entity):

•   Attributes: CustomerID (Primary Key), Name, Address, etc.

Loan:

•   Attributes: LoanNumber , Amount, Interest Rate, etc.

Question 1 : If ‘Loan’ is to be a weak entity here does it necessarily imply that two customers may have same ‘Loan Number’? Otherwise ‘LoanNumber’ can identify the relation.

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Alternatively consider the following entities in a relation ;

Customer (Strong Entity):

•   Attributes: CustomerID (Primary Key), Name, Address, etc.

Branch (Strong Entity):

•   Attributes: BranchID (Primary Key), Location, Manager, etc.

Loan :

•   Attributes: LoanNumber, Amount, Interest Rate, etc.

Question 2: If ‘Loan’ is to be a weak entity here does it imply that, Customers in two branches or more branches may have the same loan number?

1 Answer 1

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You're asking the wrong question(s). Making LoanNumber unique won't make Loan a strong entity. A loan cannot exist without at least one customer taking it, and perhaps without a branch providing it; this is what makes it a weak entity.

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