2nd Generation: Meta-Data Protocols

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.)