er.txt

来自「ssd7考试exam2,绝对有用~欢迎下载」· 文本 代码 · 共 35 行

*************Entities***************
Branches: 
	Branches_id(PK)
	Name
	Assert

Accounts:
	Accounts_id(PK)
	Balance

Customers:
	Customers_id(PK)
	Name
	Telephone
	Mail Address
	Address

*************Weak Entities***************
Transactions:
	    Transactions_id(PK)
	    Operation
	    Amount
	    Date
	    ServeBranch

*************Relationships***************
1.Has:<Branches,Accounts>,1:N,TOTAL/TOTAL
2.Hold:<Customers,Accounts>,1:N,TOTAL/TOTAL
3.Attend:<Accounts,Transactions>,1:N,PARTIAL/TOTAL 


*************Assumption*************** 
1)Each custoer has at least one account
2)one branch can have no account