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Re: Nested Sets vs. Nested Intervals

From: vc <boston103_at_hotmail.com>
Date: 9 Nov 2005 10:20:30 -0800
Message-ID: <1131560430.049560.186920@o13g2000cwo.googlegroups.com>

amado.al..._at_netcabo.pt wrote:
> > Calling Codd's work a myth is cute, but can you offer any technical
> > argument in favour of "graph-based systems" in addtion to what has been
> > rehashed on this newsgroup many times and besides "I say so" ?
>
> I don't recall the arguments in Codd's original article of 1970 or so.
> Maybe I'll take a relook next time I stop by the University library.
> Anyway the following holds.
>
> Some semantic domains are better modelled with graphs and trees than
> with relations.

Before going any farther, let's get our definitions straight in order to prevent mutual misunderstanding. Please define the "semantic domain".

>The idioms for trees and graphs in SQL is extremely
> convoluted to say the least (the word "pathetic" comes to mind).

The tools for treating tree-like structures in RDBs are pretty straightforward, there is nothing "convoluted" or "pathetic" about them. In addition to what has already been suggested, every major database has some recursive query implementation that lets the OP solve his problem easily.

>The
> original problem in this thread is an concrete example.

See above.

>
> Relational star people themselves recognized shortcomings of the
> relational theory for semantic modelling.

Who are "relational star people" ? Also, please define "semantic modelling" .

> This was a major factor in
> the creation of the Entity-Relationship model. And guess what: the E-R
> is a graph-based model.

So what ? Chen's E-R model is *not* the relational model . E-R models can be mapped to relational models or non-relational models.

>(Not to mention UML class diagrams, but I know
> what you'll say: these are for programs, not data.)

Let's not mention UML ;)

>
> There's graph-based and graph-based. As you I also don't subscribe to
> the socalled "hierarchical" and "network" models as they are often
> presented in relational circles.

If you do not subscribe to, say, the network model, then you can probably spell out how the/(a) graph-based model is different from the network model.

>They seem to be a heritage of Codasyl
> and alike systems of the 1960's. Fortunately others kept researching
> and have come up with much better graph-based models e.g. Resource
> Description Framework and even XML.

How is RDF or XML different from the network model ? Received on Wed Nov 09 2005 - 12:20:30 CST

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