I have just watched a pretty nifty presentation (courtesy of Babelfish) about the 10 dimensions of our existence (a 'la String Theory) when it dawned on me that similar thinking can be applied to the Web :-)

    Dimension 1 = Interactive Web (Visual Web of HTML based Sites aka Web 1.0)
    Dimension 2 = Services Web (Presence based Web of Services; a usage pattern commonly referred to as Web 2.0)
    Dimension 3 = Data Web (Presence and Open Data Access based Web of Databases aka Semantic Web layer 1)
    Dimension 4 = Ontology Web (Intelligent Agent palatable Web aka Semantic Web layer 2)

Hopefully, I can expand further :-)