XML

The well-known HTML was the foundational language for web development. HTML is primarily used for data presentation but unsuitable for describing data structures. The basic function of HTML is to define how information is displayed on the web (e.g., font size, type, tables, paragraphs).

XML (eXtensible Markup Language) is a text-based descriptive language that carries structural information about the data. XML is a web-adapted version of SGML (Standard Generalized Markup Language ISO 8879). Although XML is sometimes referred to as a programming language, it is actually a meta-language, meaning it can be used to describe other languages.

Three Key Features of XML

1. Extensible: You can declare your own elements, making it flexible.

2. Markup: It is a markup language because elements are distinguishable by specific tags.

3. Language: It has a fixed vocabulary and syntax.

The fundamental difference between HTML and XML is that you can define your own tags in XML. HTML works with a predefined set of tags, whereas XML allows the creation of custom tags.

Languages Created in XML for Specific Problem-Solving and Generalization

- XSL: A formatting language specifically designed for processing XML data.

- XHTML: eXtensible HyperText Markup Language. [Learn more about XHTML](http://www.w3schools.com/xhtml/).

- WAP: The language for mobile communication. [WAP/WML Reference](http://www.w3schools.com/wap/wml_reference.asp).

- SMIL: A standard multimedia description language that enables advanced multimedia and web displays. [Learn more about SMIL](http://www.w3schools.com/smil/smil_intro.asp).

- XSL Patterns: A query language that enables efficient searches in XML documents.

- SVG: Scalable Vector Graphics for describing 2D vector graphics. [Learn more about SVG](http://www.w3.org/TR/voicexml20/).

- VoiceXML: Used for speech recognition, internet voice transmission, and audio compression. [Learn more about VoiceXML](http://www.w3.org/TR/voicexml20/).

- MathML: A language for describing mathematical formulas. [Learn more about MathML](http://www.w3.org/TR/REC-MathML/).

This provides an overview of XML's capabilities, applications, and its differences from HTML.