Meta-data: "data about data" (Web resources).
All of these systems provide some "data about data."
- SGML/XML (structure meta-data)
- CSS/Aural-CSS (presentation meta-data)
- PICS (numerical annotation meta-data)
- RDF (assertions/descriptions meta-data)
(Any data that has a referent is meta-data. The definition of meta-data and semantics
are dependent on the application and respective position of other layers.)