<!DOCTYPE bank [
	<!ELEMENT bank (customer, account_type+)+>
	<!ELEMENT customer EMPTY>
	<!ATTLIST customer 
		customer_num ID #REQUIRED>
<!-- 
	A stipped-down example to show the use of IDREF
	account_type is not a child of account
	But account_type has a reference to an account
-->
	<!ELEMENT account_type (account_activity)*>
	<!ATTLIST account_type
		account_type_code (C|S) #REQUIRED
		balance CDATA #REQUIRED
		account IDREF #REQUIRED>
	<!ELEMENT account_activity EMPTY>
	<!ATTLIST account_activity
		operation_type (D|W|M) #REQUIRED
		operation_date CDATA #REQUIRED
		amount CDATA #REQUIRED>
]>

<bank>
	<!-- 
		customer with customer_num with ID value _1 
	-->
	<customer customer_num="_1"/>
	<!-- 
		accuont_type references the above account 
	-->
	<account_type
		account="_1"
		account_type_code="C"
		balance="100">
		<account_activity
			operation_type="D"
			operation_date="10:12, 03/23/08" 
			amount="99"/>
	</account_type>
	<account_type
		account="_1"
		account_type_code="S"
		balance="1"/>
	<customer
	customer_num="_2"/>
	<account_type
		account="_2"
		account_type_code="C"
		balance="1">
	</account_type>
</bank>

