Recently I have been looking at older work on 'Semantic' or 'Conceptual' Data Modeling, it seems to have been an evolution of the relational approach, essentially to try to put more smarts into the database. It actually seems to have started with Codd back in around 1970 who proposed an new approach (RM/T (Relational Model/Tasmania)) but subsequently taken up mostly by others.
I can mention the Xplain data language and DBMS of Johan ter Bekke, which seems like a forgotten thing now (and I'm trying to understand why).
But more recently the Object Role Modeling (ORM (somewhat unfortunate)) of Terry Halpin seems very the modern counterpart of this conceptual approach, in the database context at least.
Halpin now certainly seems to be going in the hybrid database direction you are suggesting with a new database system called 'LogicBlox'. I am just starting to read his
Information Modeling and Relational Databases. Second Edition (which does
seem largely about ORM and it merits), but that is pre-LogicBlox.
I don't really know much about the RDF world, but am starting to learn, at this point it strikes me as being very powerful in terms of taking data from anywhere and making use of it (the vision of TBL), but that from an 'ordinary' user perspective the tools are not that friendly, which is not so surprising, its essentially trying to bring AI to the masses (this paper discusses the problem:
http://swui.semanticweb.org/swui06/papers/Karger/Pathetic_Fallacy.html).
My key point is this: that from a cost-benefit perspective XML databases seem to have a lot of merit, if the data starts out in a hierarchical format and can be managed and used for its purposes (by creating information using XQuery) then there is little merit in normalising it. In fact, from a data user perspective, one who is not that familiar with the eventual relational model design, but who understands how the data was collected (essentially has a conceptual model), I think it adds significantly to the cost.
It seems that since the relational approach and SQL were invented, Moores Law, and the web, have totally flipped the economic equation. We can now use computing power to make sense of messy denormalised data quite well. To me using conceptual models as the interface to such data now seems like a good thing. So maybe its not hybrid databases but smarter clients that are needed? I have liked the 'info-space' ideas that Hans-Juergen Rennau has put forward in this regard, a kind of navigational approach to data in my view.
I hope some of this is of interest.
Thanks
Steve Cameron
