DTD Attribute Types - IDREF

The attribute type of IDREF is used for referring to an ID value of another element in the document.

Syntax:

Code
<!ATTLIST element_name attribute_name IDREF default_value>

Example:

Code
<!ATTLIST employee employee_id ID #REQUIRED manager_id IDREF #IMPLIED>

Valid XML - The following XML document would be valid, as it conforms to the above DTD:

Code
<employees> <employee employee_id="e10001" manager_id="e10002"> <first_name>Homer</first_name> <last_name>Flinstone</last_name> </employee> <employee employee_id="e10002"> <first_name>Fred</first_name> <last_name>Burns</last_name> </employee> </employees>

Invalid XML - The following XML document would be invalid. This is because the "manager_id" attribute of the second element contains a value that isn't the same as a value of another element that contains an attribute with a type of ID:

Code
<employees> <employee employee_id="e10001" manager_id="e10002> <first_name>Homer</first_name> <last_name>Flinstone</last_name> </employee> <employee employee_id="e10002" manager_id="e10003> <first_name>Fred</first_name> <last_name>Burns</last_name> </employee> </employees>

• << Type: ID
• Type: IDREFS >>

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