Example

Consider two entity classes, BankAccount and BankTransaction, where BankAccount. accountNo is a foreignkey on BankTransaction. That is, the BankTransaction table (txAccountNo) must have a record on the BankAccount table with a matching accountNo value.

The tables below illustrate these two classes where the foreignkey would be between their key attributes:

• entity class: BankAccount

  Attribute	Domain
  key accountNo	ACCOUNT_NO
  details clientID	CLIENT_ID
  details branchLocation	BRANCH_LOCATION
  details currentBalance	MONEY
  details lastTransaction	DATE_TYPE
  details lastStatement	DATE_TYPE

• entity class: BankTransaction

  Attribute	Domain
  key txAccountNo	ACCOUNT_NO
  details txID	TX_ID
  details transactionDate	TX_DATE
  details transactionType	TX_TYPE
  details transactionAmount	TX_AMOUNT

This foreign key results the following DDL being generated (Oracle SQL shown):

ALTER TABLE BankTransaction ADD(
  FOREIGN KEY (txAccountNo)
  REFERENCES BankAccount(accountNo));