Discover Extensible Markup Language (XML). From the early standard for web data exchange to its current role at the core of complex document structures and industry protocols.
XML (Extensible Markup Language) is a markup language used to structure electronic documents. It was designed to carry and store data, focusing on what data is, whereas HTML focuses on how data looks.
While JSON dominates Web APIs, XML remains irreplaceable in many critical domains.
The standard format for Java Spring, Android layouts, Maven (pom.xml), and major enterprise softwares.
The foundation for SOAP, SAML, RSS/Atom, and Microsoft Office documents (OpenXML).
Exchanging complex data between heterogeneous systems with high rigor and validation capabilities.
Why does XML remain the choice for complex systems?
Allows users to define their own tags, adapting to any industry or domain data requirement.
Clear structure where tags describe data meaning directly, ideal for long-term archiving.
Strong type checking via DTD or XSD (Schema) ensures data integrity and accuracy.
Decades of mature toolchains (XPath, XSLT, DOM) for complex queries and transformations.
XML syntax is stricter than HTML; it must be 'well-formed'.
Every XML document must contain exactly one root element that is the parent of all other elements.
Every opening tag must have a corresponding closing tag (<tag></tag>) or be self-closing.
In XML, attribute values must always be enclosed in quotes (single or double).
Tags must be closed in the reverse order they were opened. Example: <b><i>text</i></b>.
<?xml version="1.0" encoding="UTF-8"?>
<root>
<item id="1">
<name>Sample Item</name>
<properties>
<active>true</active>
<value>42</value>
</properties>
</item>
</root>Compare XML with other popular formats to see its strengths and limitations.
| Feature | XML | JSON | HTML | YAML |
|---|---|---|---|---|
| Primary Use | Store/Carry Data | Lightweight Exchange | Display Data / UI | Config / Readability |
| Syntax Rigor | Very High (Strict) | High (Strict) | Low (Forgiving) | Medium (Indent-based) |
| Comments | Yes (<!-- -->) | No | Yes (<!-- -->) | Yes (#) |
| Validation | Strong (Schema/XSD) | Basic (JSON Schema) | No | No native validation |
Guidelines for writing high-quality and maintainable XML.
Always start your document with <?xml version="1.0" encoding="UTF-8"?>.
Use child elements for multi-line or complex data; attributes are better for simple metadata.
Tag names should be descriptive. Use consistent casing (e.g., kebab-case or camelCase).
Always provide an XSD or DTD for production or public data to enforce standards.
Not at all. While JSON replaced it for common web APIs, XML remains the backbone of enterprise systems, document software, and complex validation workflows.
They are relatives; both derived from SGML. XML describes data contents, while HTML describes presentation and UI layout.
Schemas automatically verify data against business rules, significantly reducing error-handling costs between disparate systems.