HTML & XHTML: The Definitive Guide, 5th Edition

Building an XML DTD

Now that we’ve emerged from the gory details of XML DTDs, let’s see how they work by creating a simple example. You can create a DTD with any text editor and a clear idea of how you want to mark up your XML documents. You’ll need an XML parser and processing application to actually interpret and use your DTD, as well as a style sheet to permit XML-capable browsers to display your document.

An XML Address DTD

Let’s create a simple XML DTD that defines a markup language for specifying documents containing names and addresses. We start with an address element, which contains other elements that tag the address contents. Our address element has a single attribute indicating whether it is a work or home address:

<!ELEMENT address (name, street+, city, state, zip?)>
<!ATTLIST address type (home|business) #REQUIRED>

Voila! The first declaration creates an element named address that contains a name element, one or more street elements, a city and state element, and an optional zip element. The address element has a single attribute, type, that must be specified and can have a value of either home or business.

Let’s define the name elements first:

<!ELEMENT name (first, middle?, last)>
<!ELEMENT first (#PCDATA)>
<!ELEMENT middle (#PCDATA)>
<!ELEMENT last (#PCDATA)>

The name element also contains other elements — a first name, an optional middle name, and a last name — each of which are defined in the subsequent DTD lines. These three elements have no nested tags and contain ...