One of the advantages of storing an RDF representation in an RDBMS is that you’ll never (hardly ever?) need to make a schema change in the RDBMS - because the domain is not represented using tables - tables are solely used for storage of RDF triples.
I totally fail to get this. Why would you use an RDBMS in the first place, then?
I’ve recently become a big fan of good old relational databases. Any time I see some meta technology, I point to the appropriate layer in an RDBMS and point out that it’s already there, it’s tried and tested and hardened in 20 years, interoperable, interchangeable, available for free and for big money and there’s plenty of skilled people available … but this kind of usage seems to me like using one table for classes and one for objects (or rather, their attributes) and then pointing out how cool it is you never have to make schema changes :-)