Re: foundations of relational theory? - some references for the truly starving

"Anthony W. Youngman" <thewolery_at_nospam.demon.co.uk> wrote in message news:<fHrE46GYsFo$EwWN_at_thewolery.demon.co.uk>...
> In article <CUYmb.86063$Ms2.64480_at_fed1read03>, daveb
> <davebest_at_SuPsAaM.net> writes
> >"Ross Ferris" <ross_at_stamina.com.au> wrote in message
> >news:26f6cd63.0310260541.7a6a9af9_at_posting.google.com...
> >> "Bob Badour" <bbadour_at_golden.net> wrote in message
> news:<GumdnaAjFvrJmQaiU-KYvg_at_golden.net>...
> >> > The values in a foreign key reference are redundant because they appear
> in
> >> > multiple relations. In this case, the redundancy is appropriate and
> >> > necessary to represent the data.
> >>
> >> Interesting "admission", or at least an observation. Of course this
> >> redundancy is ONLY necessary because of the "flat earth" nature of SQL
> >> implementations.
> >>
> >> If the data were stored in a multi-valued database, or even an XML
> >> data store, then the redundant data could be removed.
> >
> >No, you have merely encoded the redundancy in the structural relationship.
> >
> Where? There is no key (foreign or otherwise) with which to do the link,
> because there is no need to do a link.
>
> So yes there is a structural relationship, but there is no redundancy
> because no information is stored - it is IMplicit in the data store, not
> EXplicit.
>
> Cheers,
> Wol

The foreign key is in the logical model. Any nested relation has a primary key consisting of the primary key columns of the containing relation (and which form a foreign key to it) plus its own primary key columns. In Pick, the primary key of a MV element is the primary key of the record plus its array index.

A relational database with relation-value (nested) attributes can choose to physically store them clustered with the containing relation, and so does not have to physically store the redundant columns.

The logical model of the data can be thought of as the API which a program uses to access the data. This is distinct from the way it is physically stored on the disk, which can be anything the vendor chooses, including the Pick method of value-encoded variable-length strings (so long as this representation is not exposed by the API).

Dave Received on Mon Nov 03 2003 - 22:05:24 CET