Sams Teach Yourself XML in 21 Days

By Steven Holzner

• Table of Contents
  • About the Author
  • Acknowledgments
  • We Want to Hear from You!
  • Introduction
  • Part I: At a Glance
  • Day 1. Welcome to XML
  • Day 2. Creating XML Documents
    • Choosing an XML Editor
    • Using XML Browsers
    • Using XML Validators
    • Creating XML Documents Piece by Piece
    • Creating Prologs
    • Creating an XML Declaration
    • Creating XML Comments
    • Creating Processing Instructions
    • Creating Tags and Elements
    • Creating CDATA Sections
    • Handling Entities
    • Summary
    • Q&A
    • Workshop
  • Day 3. Creating Well-Formed XML Documents
  • Day 4. Creating Valid XML Documents: DTDs
  • Declaring Attributes in DTDs
  • Day 6. Creating Valid XML Documents: XML Schemas
  • Day 7. Creating Types in XML Schemas
  • Part I. In Review
  • Day 8. Formatting XML by Using Cascading Style Sheets
  • Day 9. Formatting XML by Using XSLT
  • Day 10. Working with XSL Formatting Objects
  • Part II. In Review
  • Part III: At a Glance
  • Day 11. Extending HTML with XHTML
  • Day 12. Putting XHTML to Work
  • Day 13. Creating Graphics and Multimedia: SVG and SMIL
  • Day 14. Handling XLinks, XPointers, and XForms
  • Part III. In Review
  • Part IV: At a Glance
  • Day 15. Using JavaScript and XML
  • Day 16. Using Java and .NET: DOM
  • Day 17. Using Java and .NET: SAX
  • Day 18. Working with SOAP and RDF
  • Part IV. In Review
  • Part V: At a Glance
  • Day 19. Handling XML Data Binding
  • Day 20. Working with XML and Databases
  • Day 21. Handling XML in .NET
  • Part V. In Review
  • Appendix A. Quiz Answers

Creating Prologs

Prologs appear at the beginning of XML documents, and contain information about the rest of the document. A prolog can contain XML declarations, XML comments (which describe the document), processing instructions, whitespace, and doctype declarations (doctype declarations are DTDs, which we'll see in Days 4 and 5). You don't need a prolog in an XML document for the document to be well formed. However, W3C says you should include at least an XML declaration in all XML documents.

There's a sample prolog at the beginning of this XML document containing an XML declaration, a processing instruction, and a DTD (which is stored in a <!DOCTYPE> element):

   <?xml version = "1.0"?>

   <?xml-stylesheet type="text/css" href="ch_02.css"?>

   <!DOCTYPE document [

   <!ELEMENT document (employee)*>

   <!ELEMENT employee (name, hiredate, projects)>

   <!ELEMENT name (lastname, firstname)>

   <!ELEMENT lastname (#PCDATA)>

   <!ELEMENT firstname (#PCDATA)>

   <!ELEMENT hiredate (#PCDATA)>

   <!ELEMENT projects (project)*>

   <!ELEMENT project (product,id,price)>

   <!ELEMENT product (#PCDATA)>

   <!ELEMENT id (#PCDATA)>

   <!ELEMENT price (#PCDATA)>

   ]>
<document>
    <employee>
        <name>
            <lastname>Kelly</lastname>
            <firstname>Grace</firstname>
        </name>
        <hiredate>October 15, 2005</hiredate>
        <projects>
            <project>
                <product>Printer</product>
                .
                .
                .

The first item in a prolog should always be an XML declaration, and you'll take a look at this item next.

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