Semantic Web Layer Cake

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)

Trust
- authentication, trustworthiness of statements
Logic and Proof
- establish truth of statements, infer unstated facts
Ontology
- vocabularies, shared meanings e.g. DublinCore, WebOntologyLanguage (OWL, which has some elements of the layer above as well)
RDF Schema (RdfSchema)
- RDF resource types
RDF (ResourceDescriptionFramework)
- meta data, say anything about anything
XML Schema (XmlSchema)
- data types and structure
XML (ExtensibleMarkupLanguage)
- common syntax

Notes:

RDF can be respresented in other ways than XML (see RdfTriples).
The schema layers can be regarded as providing the framework for the layer immediately above.
- e.g. RDF can be expressed as an XML Schema.
- also DublinCore can expressed as an RDF Schema and also in ExtensibleMarkupLanguage without RDF.

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.