DTD-Attributes

Declaring Attributes

The ATTLIST declaration defines the element having a attribute with attribute name , attribute type , and  attribute default  value. An attribute declaration has the following syntax:

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

DTD example:

XML example:

Attribute-type

The attribute-type can be one of the following:

Default-value

The default-value can be one of the following:

DTD Example:

<!ELEMENT Scale EMPTY>
<!ATTLIST Scale length CDATA "0">

In the example above, the DTD defines a "Scale" element  to be  empty with a "length " attribute of  type CDATA . If no length is specified, it has a default value of 0.

Valid XML:

REQUIRED

Syntax

<!ATTLIST element-name attribute_name attribute-type #REQUIRED>

DTD Example

Valid XML:

Invalid XML:

<person />

Use the #REQUIRED keyword if you don't have an option for a default value, but still want to force the attribute to be present.

IMPLIED

Syntax

<!ATTLIST element-name attribute-name attribute-type #IMPLIED>

DTD Example

Valid XML:

Valid XML:

<emergency/>

Use the #IMPLIED keyword if you don't want to force the author to include an attribute, and you don't have an option for a default value.

FIXED

Syntax

<!ATTLIST element-name attribute-name attribute-type #FIXED "value">

DTD Example

Valid XML:

Invalid XML:

<Client="LotusIndia" />

Use the #FIXED keyword when you want an attribute to have a fixed value without allowing the author to change it. If an author includes another value, the XML parser will return an error.

Enumerated Attribute Values

Syntax

<!ATTLIST element-name attribute-name (en1|en2|..) default-value>

DTD Example

XML example:

<reciept type="check" />
or
<reciept type="cash" />

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