In the four posts in this series that explains Structured Authoring looked at:

1. Understanding Structured Authoring
2. Structured Authoring: Introducing XML
3. Structured Authoring: Defining the Content Structure
4. Structured Authoring: The Role of the DTD/Schema

In this post, we look at a Document Type Definition (DTD), which is the formal definition of a content structure.

Consider the following image which shows a sample DTD for an email.

This DTD specifies that:

• an email must have three elements; address, subject, and body.
  • address must contain one sender and one receiver element.
    • the sender must contain one emailaddress.
    • the receiver must contain a to element, and an optional cc and/or bcc element.
    • the to, cc, and bcc elements must contain one or more emailaddress elements.
    • the emailaddress element contains text.
  • the subject element contains text.
  • the body element must contain a salutation, message, and signature.
    • the salutation element contains text.
    • the message element must start with a para element.
      • After the initial para element, there can be number of para, list, or image elements and in any order.
      • the para element contains text.
      • the list element must contain one or more listitem elements.
        • the list element has an attribute type which can be given the value bullet or number, with bullet being the default value.
        • the listitem element contains text.
      • the element image is an empty element with a mandatory attribute href which contains text.
  • the signature element contains one or more para elements.