ER diagram for a commercial bank

For a more detailed explanation of each step, reading the article(Steps to create ER Diagram) is strongly recommended.

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1. Identify the Entities

The list of entities is provided clearly in the given question.

The entities are:

  • Depositor
  • Account
  • Loan
  • Branch

 Step-1-Entities-Bank-ER-Diagram

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    2. Figure out Relationships and Participation Constraints

    Step-2-Relationships-Participation-Constraints-Bank-ER-Diagram

    Based on our knowledge of the functioning of Banks, we assume the following Relationships and Participation Constraints.

     

    Depositor holds Account

    • Every Depositor must have at least one Account. Hence, the participation of the Depositor in the relationship holds is Total.
    • Every Account must be owned by at least one Depositor. Hence, the participation of the Account in the relationship holds is Total.

     

    Account is created by Branch

    • Every Account must be created by at least one Branch. Hence, the participation of the Account in the relationship 'created by' is Total.
    • Some Branches may not have created any Accounts. Hence, the participation of the Branch in the relationship 'created by' is Partial.

     

    Note: We are representing Loan as a Weak Entity. The relationship borrows is an Identifying Relationship.

    Depositor borrows Loan

    • Some Depositors may borrow a Loan. Some may not. Hence, the participation of the Depositor in the relationship borrows is Partial.
    • Every Loan is borrowed by at least one Depositor. Hence, the participation of the Loan in the relationship borrows is Total.

     

    Loan is lent by Branch

    • Every Loan is lent by at least one Branch. Hence, the participation of the Loan in the relationship 'lent by' is Total.
    • A Branch may or may not lend Loan. Hence, the participation of the Branch in the relationship 'lent by' is Partial.

     

     

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    3. Specify Cardinality Constraints

    Step-3-Cardinality-Constraints-Bank-ER-Diagram

    Assumptions

    A Depositor can hold multiple Accounts. An Account can be held by multiple Depositors. The concept of Joint Account is used here. Thus, "Depositor holds Account" is a Many-to-Many relationship.

    An Account cannot be created by more than one Branch. A Branch can create multiple Accounts. Thus, "Account created by Branch" is a Many-to-One relationship.

    A Depositor can borrow multiple Loans. A Loan can be associated with multiple Depositors, through Joint Account. Thus, "Depositor borrows Loan" is a Many-to-Many relationship.

    A Loan cannot be lent by more than one Branch. A Branch can lend multiple Loans. Thus, "Loan lent by Branch" is a Many-to-One relationship.

     

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    4. List the Attributes

    We are assuming the following attributes for each entity.

    Entity Attributes
    Depositor

    D_ID

    Contact

    D_Name

    Email

    Account

    Acc_No

    Balance

    Acc_type

    Creation_date

    Branch

    B_ID

    B_Name

    Location(State, District, City)

    Loan

    Loan_No

    Amount

     

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    5. Final ER Diagram

    ER-diagram-commercial-bank: Depositor, Account, Branch and Loan

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