Purpose of a DTD

When using a DTD for an XML document (including XHTML), the DTD is there to provide structure for your documents. It is easy to write an XML document, but without the DTD, it has no syntactic meaning to the computer. For example, if you come across this portion of an XML document:

   123 Any Street
Jackson MI

While you would know it was an address, you wouldn't know whether it was an address the computer was supposed to create from a database table, if that address was for mailing, and other things. The computer, on the other hand, wouldn't see this as anything more than a string of text. If you viewed it in an XML browser, you might not get any errors, but you also wouldn't get a very interesting or useful page.

In other articles, we'll explore the inner workings of a DTD, and examine the elements that make up a DTD. You'll learn what an element, attribute, entity, and notation is and how to use them within your own DTDs. Plus, you'll learn how to read other DTDs so that you can use them in your own XML documents.