Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]
Date: Mon, 20 Jun 2005 13:33:53 +0200
Jan Hidders schrieb:
> Alexandr Savinov wrote:
>> >> No, I do not discard the RM properties and functionality. In COM you >> still can use all relational features. What I claim is that you will >> need to use them because you can reach your goal in a simpler way. COM >> is completely compatible with RM - it simply makes some mechansims >> unnecessary.
> Well, that clarifies the discussion a bit. It's pretty obvious (though
> some in this group will probably argue otherwise) that the RM as a data
> model is rather clunky and low-level and that it is easy to come up with
> a data model that is more elegant and expressive. Many already have. But
> one should keep in mind that this is actually a feature, not a bug,
> because the point of RM is not just to be a good data model, its purpose
> is to be a good data model for the logical layer of the DBMS. That's
> similar, but not exactly the same.
> This means two things. The first is that you should not call your model
> a database model, because that is not it's purpose; its purpose is to be
> a (higher level) data model. As a consequence it is not that useful to
> compare it to the RM. What you should compare it to are other data
> models that have more or less the same purpose, such as Shipman's FDM,
> Halpin/Nijssen's ORM/NIAM, Abiteboul/Hull's IFO, all kinds of extended
> ER models (e.g. Thalheims HERM), Kuper/Vardi's LDM, and probably many
> more I cannot think of right now.
> After looking a bit longer at your model I think FDM might be especially
> relevant, and probably even more so in it's modern incarnation that is
> the data model for Description Logics. It's very simple. Its
> formalization can be given in half a page or less. I can explain it to
> my students and probably to most participant in this group in 10
> minutes. It has an associated logic that is well know, very expressive
> and has nice computational properties. It doesn't have the limitation
> that the schema graph should be a lattice, but if you would so desire
> you could probably easily add a notion of "spanning lattice" that would
> allow the automatic guessing of paths between distant classes.
> As far as I understand your model the basic structure is very similar to
> that of FDM-like data models (basically ER restricted to binary
> relationships) and what you add to that is an interesting enhancement
> but I wouldn't describe it as a completely different paradigm or a
> radical new data modelling philosophy. Note btw. that in FDM the problem
> of defining the join conditions is actually not that much of a problem
> anyway, certainly not as much as it is in the RM, because you use path
> expressions which are a much more compact and natural way of describing
> those anyway. So you would actually only solve a minor problem. Still,
> like I said, not uninteresting, and combined with the stuff on
> aggregation and propagation you might actually be on to something.
Thanks for the substantial comment and for the reference to FDM model. I printed it and will read later.
Currently "Dimensionality modelling..." is submitted to "Concept Lattices and Their Applications" (http://cla2005.inf.upol.cz).
If you know some relevant conference then I would very appreciate if you could send it to me. It is a serious problem to position such a work in the world of (scientific) borders and especially when it is not the main goal and when you are not a member of a scientific gang :-)Received on Mon Jun 20 2005 - 13:33:53 CEST