## BANK database

Q1. Consider the given ER diagram for part of a BANK database (attached for reference). Each bank can have multiple branches, and each branch can have multiple accounts and loans.

(a) List the strong (nonweak) entity types in the ER diagram.

(b) Is there a weak entity type? If so, give its name, its partial key, and its identifying relationship.

(c) What constraints do the partial key and the identifying relationship of the weak entity type specify in this diagram?

(d) List the names of all relationship types, and specify the (min,max) constraint on each participation of an entity type in a relationship type. Justify your choices.

## Sample Answer

a) The strong (nonweak) entity types in the ER diagram are:

• Bank
• Branch
• Account
• Loan

(b) Yes, there is a weak entity type in the ER diagram. It is the Account entity type. The partial key of the Account entity type is account_number. The identifying relationship of the Account entity type is the has_account relationship.

## Full Answer Section

c) The partial key and the identifying relationship of the weak entity type specify the following constraints in this diagram:

• An Account entity must be associated with a Branch entity.
• The account_number of an Account entity must be unique within its Branch entity.

Here is a more detailed explanation of each constraint:

• The first constraint states that an Account entity must be associated with a Branch entity. This is because the has_account relationship is a 1:M relationship. This means that each Branch entity can have multiple Account entities, but each Account entity can only be associated with one Branch entity.
• The second constraint states that the account_number of an Account entity must be unique within its Branch entity. This is because the account_number is the partial key of the Account entity. A partial key is a set of attributes that uniquely identifies an entity within its parent entity. In this case, the account_number uniquely identifies an Account entity within its Branch entity.

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