Next Generation HTML: XML Applications (Vocabularies)

As stated earlier, the right side of the diagram depicts specs that are all related to XML. In a sense, they are all XML applications in that they rely on XML syntax. Some are specialized markup languages, also called XML vocabularies, such as MathML (Mathematical Markup Language), a W3C recommendation, SMIL (Synchronized Multimedia Integration Language), a Proposed Recommendation, and PGML (Precision Graphics Markup Language), WIDL (Web Interface Definition Language), and CDF (Channel Definition Format), three W3C Notes. Others are more like applications layered on top of XML, such as the RDF (Resource Description Format), Metadata efforts, PICS 2.0 ( Platform for Internet Content Selection) and P3P (Platform for Privacy Preferences). However, the distinction between these two groups may not be terribly significant.

Next Generation HTML: Linking Efforts
Next Generation HTML: The Big Picture
Next Generation HTML: Netscape and Microsoft