A new and hopefully readable article on XML.com, "A Relational View of the Semantic Web". The main reason is to illicit some feedback and to make a more understanble version of things like this. It also discusses whether or not to use blank nodes when mapping RDF to the relational model (which is something I first published in my thesis). It includes my take, which is no doubt influenced by Simon and working on Kowari, on the DISTINCT issue amongst others.
Update: Well if any feedback is good feedback, having positive feedback is awesome: "But it begs the question: given the relative proximity of RDF/SPARQL to the relational model, why are the Semantic Web standards not closer both syntactically and semantically to it? This is, for me, the major reason which prevents its adoption...Nice to see such a straightforward and well-referenced article outlining the Semantic Web and relational worlds in any case. Thank you."
The question raised in the comment, why not keep pushing SQL, is one I wish I had a short answer for. Often SPARQL syntax has been chosen to look like SQL. But obviously it's still different enough because it is a different domain. I still favour a clean break from SQL for that reason.
I wrote about SQL not being relational enough quite a while ago now (nearly 3 years). At the time, I think I was unaware of some of the operations in SQL like INTERSECT and EXCEPT (set difference).
Update 2: Also noted by Nova Spivacks, "Excellent Overview of Benefits of RDF and SPARQL".