2003年《数据库系统概论》期末考试试卷(B) 本试题所用到的银行企业的数据库模式如下所示:  Customer-schema=(customer-name, customer-street, customer-city)  Account-schema=(branch-name, account-number, balance)  Depositor-schema=(customer-name, account-number)  Branch-schema=(branch-name, branch-city, assets)  Loan-schema=(branch-name, loan-number, amount)  Borrower-schema=(customer-name, loan-number) 建立在这些关系模式上的数据库中的关系如下所示:  customer (Customer-schema)  account (Account-schema)  depositor (Depositor-schema)  branch (Branch-schema)  loan (Loan-schema)  borrower (Borrower-schema)