The Semantic Web is the Cake…but the Technologies are not the Layers

My last post about the relationship between Linked Data, the Semantic Web and the Semantic Web technology stack seemed to create more debate and disagreement than clarity. Not to be discouraged by this, I’ve been giving some more thought to analogies that may help to illuminate the the relationship between different concepts in the Semantic Web space. This got me thinking about the Semantic Web layer cake.

The layer cake diagram is probably one of the most used and abused images associated with the Semantic Web vision. In the diagram, each technology or concept in the Semantic Web stack is a layer, with Crypto providing some kind of irregular icing down one side. I’d like to propose a different interpretation of the Semantic Web as a cake.

In my view, the technologies aren’t layers in the finished cake, they’re the raw ingredients that must be mixed and baked to make the cake that is the Semantic Web itself. URIs are the grains of flour; an ingredient that is essential but by itself rather bland, and lacking form and coherence. RDF triples are the egg that can bind together this URI flour. This cake is taking shape, but it’s lacking flavour. In the Semantic Web cake these flavourings, such as FOAF, SIOC, or the Programmes Ontology, are concocted on a base of RDFS and OWL. Simple cakes based on one or two flavours can be very tasty, but for our Semantic Web cake to be truly delicious we want a wide range of flavours, with some dominating others in different parts of the cake.

Once we’ve baked our cake, by putting our RDF data online according to the Linked Data principles, we’ll probably want to decorate it. Perhaps some icing or cherries on top, in the form of inferred RDF triples, would make it even more delicious. With such an appealing data cake it’s inevitable that people will want to consume it, but we have to make sure that everyone can have a slice rather than letting a big data gluton run off with the cake and deprive everyone else of this treat. We need some sort of knife; preferably one like SPARQL, that allows people to help themselves to the parts of the cake they like best. Will the cake baked and decorated, and will all the tools in place, it’s time to invite some friends round (maybe even some agents) and start consuming.

(I see that Jim Hendler’s keynote at ESWC2009 will talk about the layer cake; I’m intrigued to see how he choses to serve up the analogy).

1 Response to “The Semantic Web is the Cake…but the Technologies are not the Layers”


  1. John Goodwin

    So would you prefer OWL or RIF flavoured icing? For me it seems an obvious place to start would be encourage people to maybe stick to OWL2 RL (http://www.w3.org/TR/owl2-profiles/#OWL_2_RL) for linked data ontologies? A nice simple fragment of OWL2 that can be coded using rules (I think Ivan Herman wrote a python OWL2 inference engine in an afternoon).

    Look forward to seeing an OWL2 RL reasoner in the Platform 🙂