I thought that we had talked ourselves to exhaustion and beyond over the issue of the semantic web layer cake. Apparently not. There was a paper called Functional Architecture for the Semantic Web by Aurona Gerber et al at ESWC2008.
The thrust of the matter was that for newcomers the layer cake was confusing and did not clearly indicate the architecture. Why, sure. My point is that no rearranging of the boxes will cut it for the general case.
Any diagram containing the boxes of the layer cake (i.e., URI, XML, SPARQL, OWL, RIF, Crypto, etc., etc.) in whatever order or arrangement can at best be a sort of overview of how these standards reference each other.
Such diagrams are a little like saying that a car combines the combustion properties of fuel/air mixes with the tension and compression resistance properties of metals and composites for producing motion and secondly links to Newton's laws of motion and to aerodynamics.
Not false. But it does not say that a car is good for economical commute or showing off at the strip or any number of niches that a mature industry has grown to serve.
Now, talking of software engineering, modules and interfaces are good and even necessary. The trick is to know where to put the interface.
Such a thing cannot possibly be inferred from the standards' inter-reference picture. APIs, especially if these are Web service APIs, should go where there is low data volume and tolerance for latency. For example, either inference is a preprocessing step or it is embedded right inside a SPARQL engine. Such a thing cannot be seen from the picture. Same for trust. Trust is not an after-thought at the top of the picture, except maybe in the sense of referring to the other parts.
We hear it over and over. Scale and speed are critical. Arrange the blocks of any real system as makes sense for data flow; do not confuse literature references with control or data structure.
The even-more foundational issue is the promotion of the general concept of a Web of Data.
The core idea that the Web would be a query-able collection of data with meaningful reference between data of different provenance cannot be inferred from the picture, even though this should be its primary message. Or it is better to say that the first picture shown should stress this idea and then one could leave the layer cake, in whatever version, for explaining the standards' order of evolution or inter-reference.
So, the value proposition:
Why? Explosion of data volume, increased need of keeping up-to-date, increasing opportunity cost of not keeping in real time.
What? An architecture that is designed for unanticipated joining and evolution of data across heterogeneous sources, either at Web or enterprise scale.
How? URI everything and everything is cool, or, give things global names. Use RDF. Reuse names or ontologies where can. (An ontology is a set of classes and property names plus some more.) Map relational data on the fly or store as RDF, whichever works. Query with SPARQL, easier than SQL.
So, my challenge for the graphics people would be to make an illustration of the above. Forget the alphabet soup. Show the layer cake as a historical reference or literature guide. Do not imply that this proliferation of boxes equates to an equal proliferation of Web services, for example.