• Chapter 1: Getting Started with Stylus Studio
• Chapter 2: Editing and Querying XML
• Chapter 3: Converting Non-XML Files to XML
• Chapter 4: Working with XSLT
• Chapter 5: Creating XSLT Using the XSLT Mapper
• Chapter 6: Debugging Stylesheets
• Chapter 7: Defining XML Schemas
• Chapter 8: Defining Document Type Definitions
  • What Is a DTD?
  • Creating DTDs
  • About Editing DTDs
  • About Modifiers in Element Definitions in DTDs
  • Defining Elements in DTDs
  • Defining General Entities and Parameter Entities in DTDs
  • Inserting White Space in DTDs
  • Adding Comments to DTDs
  • About Node Properties in DTDs
  • Associating an XML Document with an External DTD
  • Moving an Internal DTD to an External File
• Chapter 9: Writing XPath Expressions
• Chapter 10: Working with XQuery in Stylus Studio
• Chapter 11: Composing Web Service Calls
• Chapter 12: Accessing Relational Data as XML
• Chapter 13: Extending Stylus Studio
• Chapter 14: Stylus Studio Reference

Home > Online Product Documentation > Table of Contents > Specifying That an Element is Required in DTDs

Specifying That an Element is Required in DTDs

You specify that an element is required when you add a reference to that element in another element.

In the Tree tab, to specify that an element is required:

4. In the tool bar on the left, click New Modifier . Stylus Studio displays a drop-down menu.

7. With the modifier highlighted, click New Reference to Element in the tool bar on the left.

After you add a reference to an element, you might want to check the definition of the referenced element. To do this, right-click the reference. In the shortcut menu, click Go To Definition. Stylus Studio moves the focus to the definition of the referenced element.

Example 1

For example, suppose the title element is required, and that it is relevant only in the context of a book element. When you define the book element, you specify that it contains the title element. If you specify only the Sequence modifier, the occurrence default is assumed. The occurrence default is that there must be exactly one of the contained element. In other words, the title element is required and there can be only one. In this case, the definition of the book element is as follows:

<!ELEMENT book (title)>
               

            

The tree representation looks like this:

book
               

              

                
Sequence
                   
title
                   

                
              

            

Example 2

It is also possible for an element to be required and for more than one to be allowed. Suppose the book element must also contain at least one author element, but it can contain more than one author element. The definition of the book element is as follows:

<!ELEMENT book (title, author+)>
               

            

The tree representation looks like this:

book
               

              

                
Sequence
                   
title
                   
One or More
                   
	author