The Semantic Web Layer Cake is an idea discussed in ExplorersGuide (to the Semantic Web) p.14 and attributed to Sir TimBernersLee - see http://www.w3.org/2000/Talks/1206-xml2k-tbl/slide10-0.html. The point is that there are different layers in the SemanticWeb and that they do different things. Some of the layers can take different forms. Each of the layers is less general than the layers below it. -- JohnFletcher
The Semantic Web Layer Cake (ExplorersGuide version)
There is another version of this diagram in the book ProgrammingTheSemanticWeb in Chapter 11. This distinguishes between parts of this which are Practical semantic technologies and parts which are Future and fantasy technologies.
See also SemanticWebIsStupid