XML

What is XML?

XML (Extensible Markup Language) is a markup-based data exchange format designed to store and transport data in a structured, human-readable way. Unlike JSON, which uses a lightweight key-value structure, XML relies on tags to define its hierarchy, making it highly customizable but slightly more verbose.

What is Markup?

Markup refers to the use of tags to define the structure of a document or data, often with attributes for added context.

For example, <tag attribute="value">content</tag> is a typical markup pattern. XML leverages this to create a tree-like structure for data.

Structure of XML

An XML document consists of:

1. Prologue: Declares the XML version and encoding (e.g., <?xml version="1.0" encoding="UTF-8"?>).
2. Root Element: A single top-level element that contains everything else (e.g., <FOODList>).
3. Child Elements: Nested elements within the root.

HTML vs. XML

While HTML and XML share some similarities (both use tags), they serve different purposes:

1. Purpose:
   • HTML: Displays data (e.g., web pages).
   • XML: Stores and transports data.
2. Tags:
   • HTML: Uses predefined tags like <p> and <div>.
   • XML: Allows custom tags (e.g., <FOOD> or <ingredient>).
3. Case Sensitivity:
• HTML: Case-insensitive (<DIV> = <div>).
• XML: Case-sensitive (<book> ≠ <Book>; mismatches cause errors).

JSON vs. XML

Key differences:

• Verbosity: XML requires closing tags (e.g., </name>), making it heavier than JSON’s concise syntax.
• Parsing: JSON converts to a JavaScript object with JSON.parse(), while XML needs additional effort (e.g., using a library like xml2json in Node.js)

Why Use XML?

Real-World Use: Sitemap.xml

XML shines in applications like sitemap.xml, which lists all pages of a website for search engine crawlers. This ensures large or disconnected sites are fully indexed.