DTD Elements

Creating a DTD is quite straight forward. It's really just a matter of defining your elements, attributes, and/or entities. Over the next few lessons, I'll explain how to define your elements, attributes, and entities.

In this lesson, we'll look at the syntax for defining your XML elements.

To define an element in your DTD, you use the <!ELEMENT> declaration. The actual contents of your <!ELEMENT> declaration will depend on the syntax rules you need to apply to your element.

Basic Syntax

The <!ELEMENT> declaration has the following syntax:

<!ELEMENT element_name content_model>

Here, element_name is the name of the element you're defining. The content model could indicate a specific rule, data or another element.

• If it specifies a rule, it will be set to either ANY or EMPTY.
• If specifies data or another element, the data type/element name needs to be surrounded by brackets (i.e. (tutorial) or (#PCDATA)).

The following examples show you how to use this syntax for defining your elements.

Plain Text

If an element should contain plain text, you define the element using #PCDATA. PCDATA stands for Parsed Character Data and is the way you specify non-markup text in your DTDs.

Using this example - <name>XML Tutorial</name> - the "XML Tutorial" part is the PCDATA. The other part consists of markup.

Syntax:

<!ELEMENT element_name (#PCDATA)>

Example:

<!ELEMENT name (#PCDATA)>

<name>XML Tutorial</name>

Unrestricted Elements

If it doesn't matter what your element contains, you can create an element using the content_model of ANY. Note that doing this removes all syntax checking, so you should avoid using this if possible. You're better off defining a specific content model.

Syntax:

<!ELEMENT element_name ANY>

Example:

<!ELEMENT tutorials ANY>

Empty Elements

You might remember that an empty element is one without a closing tag. For example, in XHTML, the <br /> and <img /> tags are empty elements. Here's how you define an empty element:

Syntax:

<!ELEMENT element_name EMPTY>

Example:

<!ELEMENT header EMPTY>

<header />

Child Elements

You can specify that an element must contain another element, by providing the name of the element it must contain. Here's how you do that:

Syntax:

<!ELEMENT element_name (child_element_name)>

Example:

<!ELEMENT tutorials (tutorial)>

<tutorials>
  <tutorial></tutorial>
</tutorials>

Multiple Child Elements (Sequences)

You can also provide a comma separated list of elements if it needs to contain more than one element. This is referred to as a "sequence". The XML document must contain the tags in the same order that they're specified in the sequence.

Syntax:

<!ELEMENT element_name (child_element_name, child_element_name,...)>

Example:

<!ELEMENT tutorial (name, url)>

<tutorials>
  <tutorial>
    <name></name>
    <url></url>
  </tutorial>
</tutorials>

• << Previous Lesson
• Next Lesson >>