What is XML?
XML (Extensible Markup Language) is a markup language and file format for storing, transmitting, and reconstructing data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable.
Quick Facts
| Full Name | Extensible Markup Language |
|---|---|
| Created | 1998 by W3C |
| Specification | Official Specification |
How It Works
XML uses tags to define elements, similar to HTML but with custom tag names. Every opening tag must have a corresponding closing tag, and elements must be properly nested. XML supports attributes within tags, namespaces for avoiding naming conflicts, and schemas (XSD) for validation. While JSON has largely replaced XML for web APIs, XML remains important in enterprise systems, document formats (DOCX, SVG), and configuration files.
Key Characteristics
- Self-describing with custom tag names
- Strict syntax - must be well-formed
- Supports namespaces for element disambiguation
- Schema validation with XSD or DTD
- Supports comments, CDATA sections, and processing instructions
- Platform and language independent
Common Use Cases
- Enterprise data exchange (SOAP, EDI)
- Document formats (Microsoft Office, SVG, RSS)
- Configuration files (Maven, Android, Spring)
- Data storage and archival
- Web services (SOAP APIs)
Example
Loading code...Frequently Asked Questions
What is the difference between XML and JSON?
XML uses tags with opening/closing elements and supports attributes, comments, and schemas. JSON uses simpler key-value pairs with brackets. JSON is lighter and more common in web APIs, while XML is preferred in enterprise systems and document formats.
What does 'well-formed XML' mean?
Well-formed XML follows strict syntax rules: every opening tag must have a closing tag, elements must be properly nested, attribute values must be quoted, and there must be exactly one root element. A well-formed document can be parsed without errors.
What is the difference between XML attributes and elements?
Attributes are name-value pairs inside opening tags (<book category='fiction'>), while elements are the tags themselves with content between them. Use attributes for metadata and simple values; use elements for complex, repeatable, or hierarchical data.
What is XML namespace and why is it used?
XML namespaces prevent naming conflicts when combining XML documents from different sources. They use prefixes with URIs (xmlns:prefix='URI') to uniquely identify elements, allowing the same tag name to have different meanings in different contexts.
Is XML still relevant today with JSON being so popular?
Yes, XML remains important in enterprise systems (SOAP), document formats (DOCX, SVG, RSS), configuration files (Maven, Android), and industries requiring strict validation. Its schema support and self-describing nature make it valuable for complex data structures.