Is the entity-relationship diagram about customers and accounts correct

database-designerd

Business domain description

  • Each customer has a name, a permanent address, and a social security number.
  • Each customer can have multiple phone numbers, and the same phone number may be shared by multiple customers.
  • A customer can own multiple accounts, but each account is owned by a single customer.
  • Each account has an account number, a type (such as saving, checking, etc.), and a balance
  • The bank issues an account statement for each account and mails it to its account owner every month. As time goes on, there will be multiple statements of the same account.
  • Each statement has an issued date and a statement ID. All the
    statements of the same account have different statement IDs, but two
    different accounts could have statements with the same statement ID.
    For example, it is possible that account A has a statement with ID
    ‘123', while account B has another statement with the same ID '123'.

My entity-relationship representation

I have drawn the following entity-relationship diagram (ERD) to represent that scenario:

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Questions

  1. Can Min-Max notation be used in case of any relationships, or, just when there is an indication for that in the description?

  2. Are my many-to-many relationships portrayed correctly here?

  3. Could I properly portray the relationships among Account vs Account Statement vs StatementID?

  4. As per my assumption, Is Account Statement really a weak entity and is Has really a weak relation that is dependent on Statement ID? Is issue-date a weak key?

Best Answer

Scheme fix

IMHO you just have to pay attention on the order of cardinalities, and you should note that Issue Date is not a weak key, but it's not a key at all: in fact you could have two account statements of different people issued on the same date, so you need a foreign key (Issue Date plus Number of Account)

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