DTD Attributes IN XML

In the DTD, XML element attributes are defined with an ATTLIST declaration.

An attribute declaration has the following syntax:

<!ATTLIST element-name attribute-name attribute-type default-value>

Tthe ATTLIST declaration defines the element which can have the attribute, attribute-name is the name of the attribute, attribute-type is the type of the attribute, and the default attribute value.

The attribute-type can have the following values:

Value	Explanation
xml:	The value is predefined
ID	The value is an unique id
IDREF	The value is the id of another element
IDREFS	The value is a list of other ids
CDATA	The value is character data
NMTOKEN	The value is a valid XML name
NMTOKENS	The value is a list of valid XML names
ENTITY	The value is an entity
ENTITIES	The value is a list of entities
NOTATION	The value is a name of a notation
(eval\|eval\|..)	The value must be an enumerated value

The default-value can have the following values:

Value	Explanation
#DEFAULT value	The attribute has a default value
#REQUIRED	The attribute value must be included in the element
#IMPLIED	The attribute does not have to be included
#FIXED value	The attribute value is fixed

Attribute declaration example:

<?xml version=”1.0″ encoding=”ISO-8859-1″?>
<!DOCTYPE email [
<!ELEMENT email (sender,recipient,subject,message)>
<!ATTLIST email priority CDATA “normal”>
]>
<email priority=’high’>
</email>

In the above example, the element email is defined to be an empty element with the attributes propriety of type CDATA. The priority attribute has a default value of “Normal”.

Click here to view the example.

Enumerated attribute values

Syntax:

<!ATTLIST element-name attribute-name (eval|eval|..) default-value>

DTD example:

<!ATTLIST payment mode (check|cash) “cash”>

XML example:

<payment mode=”check”>
or
<payment mode=”cash”>

Use enumerated attribute values when you want the attribute values to be one of a fixed set of legal values.

Fixed attribute value

<?xml version=”1.0″ encoding=”UTF-7″?>
<!DOCTYPE ebiz [
<!ELEMENT ebiz (associate_details,emp_details,sponser_details)>
<!ATTLIST ebiz companysite CDATA #FIXED “http://www.ebizel.com”>
]>
<ebiz>
</ebiz>

Use a fixed attribute value when you want an attribute to have a fixed value that the author can not change. If an author includes another value, the XML parser will return an error.

Required attribute

<!ELEMENT payment (amount+,duration+)>
<!ATTLIST payment mode CDATA #REQUIRED>

XML example:

<payment mode=”cash”></payment>

Use a required attribute if you don’t have an option for a default value, but still want to force the attribute to be present. The required (#REQUIRED) attribute force the document author to use the attribute.

Implied attribute

<!ELEMENT addressdetails (address+,city?,state,pin)>
     <!ATTLIST addressdetails communication_mode CDATA #IMPLIED>
      <addressdetails communication_mode=”post”>
      </addressdetails>

Use an implied attribute if you don’t want to force the author to include an attribute and you don’t have an option for a default value either.