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Re: relational mapping?

From: Jan Grant <Jan.Grant@bristol.ac.uk>
Date: Fri, 4 May 2001 10:07:26 +0100 (BST)
To: Seth Russell <seth@robustai.net>
cc: Danny Ayers <danny@panlanka.net>, Www-Rdf-Logic <www-rdf-logic@w3.org>, RDF-Interest <www-rdf-interest@w3.org>
Message-ID: <Pine.GSO.4.31.0105041002560.2082-100000@mail.ilrt.bris.ac.uk>
On Thu, 3 May 2001, Seth Russell wrote:

> From: "Jan Grant" <Jan.Grant@bristol.ac.uk>
>
> > > No doubt you are aware of the list of these recorded at [1], to which
> list I
> > > have added the structure diagrammed at [2].
> > >
> > > [1] http://www-db.stanford.edu/~melnik/rdf/db.html
> > > [2] http://robustai.net/mentography/SemStructure.gif
> >
> > Neat; but these seem to be "storing RDF in RDBMS" as opposed to
> > "producing RDF from a (legacy?) RDBMS"
>
> Ok sorry, I see now you want to go the other direction.  I saw somewhere
> (forget where) the idea that you could do it this way:
>
> A RDF Class represents a Relational Table.
> A RDF instance node represents a Relational Record.
> The columns in the Relational table are the property arcs on the instance
> nodes.
>
> Hope that helps.

Yep; I think this is what both Danny and I intimated was a "naieve"
approach. It has the advantage of "just working"* for at least
_producing_ RDF from an RDBMS. But it doesn't really capture any
sematics that the RDBMS schema may be trying to describe. A row in a
table may hold details (conceptually) about one or more resources
(possibly just one, depending on which NF it is in). The use of a middle
table to model many-to-many tables has multiple potential
representations in RDF; similarly, there are potentially several
representations of a many-to-one relationship (just using arcs, or using
collections if that's more appropriate). To make these choices, you need
to really be aware of what the RDBMS schema is trying to capture to make
informed decisions about producing RDF from these.

jan

* "just" = "simply" as opposed to "barely"

-- 
jan grant, ILRT, University of Bristol. http://www.ilrt.bris.ac.uk/
Tel +44(0)117 9287163 Fax +44 (0)117 9287112 RFC822 jan.grant@bris.ac.uk
Usenet: The separation of content AND presentation - simultaneously.
Received on Friday, 4 May 2001 05:09:42 GMT

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