Defining Structure Rules in a Sample DTD

This topic is part of a sequence that starts with Creating a Sample DTD.

To specify the rules for the structure of the book element:

1. Click the book node in the DTD tree if it is not already selected.

2. Click New Modifier

3. In the drop-down list that appears, scroll down and double-click Sequence. This indicates that the book element can include one or more elements.

4. Click New Reference to Element

5. Type title in the entry field and press Enter.

Because the reference to the title element appears immediately after the Sequence modifier, the DTD editor assumes that the default behavior is what is wanted. That is, the book element must contain exactly one instance of the title element.

6. Click the Sequence modifier.

7. Click New Modifier

8. Double-click One or More. (There can be one or more author elements in each book element.)

9. Click New Reference to Element

10. Type author in the entry field and press Enter.

At this point, the definition of the book element is complete, and the tree diagram of bookstore.dtd should look like this:

Figure 50. Early Steps of bookstore.dtd

However, you have not yet specified that you want the book element itself to be optional. You need to do this in the element that references the book element. For example, suppose the bookstore element is the root element in XML documents that use this DTD. Further suppose that you want the book element to be a child of the bookstore element.