Introduction to XML

What is XML?

XML (eXtensible Markup Language) is a markup language designed to store, transport, and structure data. Unlike HTML (which displays data), XML is focused on describing data.

• Defined by W3C in 1998
• Both human-readable and machine-readable
• Platform-independent, self-describing

XML Syntax Rules

<?xml version="1.0" encoding="UTF-8"?>
<bookstore>
    <book category="fiction">
        <title lang="en">The Great Gatsby</title>
        <author>F. Scott Fitzgerald</author>
        <year>1925</year>
        <price>12.99</price>
    </book>
    <book category="technology">
        <title lang="en">Clean Code</title>
        <author>Robert C. Martin</author>
        <year>2008</year>
        <price>35.00</price>
    </book>
</bookstore>

XML Rules

1. Every XML document must have a root element
2. All elements must have a closing tag
3. Tags are case-sensitive (<Name> ≠ <name>)
4. Elements must be properly nested
5. Attribute values must be quoted
6. Special characters must use entities

XML vs HTML

XML Elements and Attributes

<!-- Element with attributes -->
<student id="101" grade="A">
    <name>Alice</name>
    <email>alice@example.com</email>
    <marks>
        <subject name="Math">95</subject>
        <subject name="Science">88</subject>
    </marks>
</student>

XML Special Characters (Entities)

XML Namespace

<root xmlns:h="http://www.w3.org/TR/html4/"
      xmlns:f="http://www.example.com/furniture">
    <h:table>
        <h:tr><h:td>HTML Table</h:td></h:tr>
    </h:table>
    <f:table>
        <f:name>Dining Table</f:name>
    </f:table>
</root>

XML Applications

• RSS/Atom feeds – news syndication
• SOAP web services – enterprise web services
• SVG – scalable vector graphics
• Office Open XML – .docx, .xlsx files
• Android layouts – UI XML files
• Maven/Gradle – build configuration

Key Takeaway: XML is a universal data format for storing and transporting structured data. Its strict syntax rules (proper nesting, closing tags, quoted attributes) make it reliable but verbose compared to JSON.