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Home -> Community -> Usenet -> comp.databases.theory -> Re: Stored fields ordered left to right
"Jonathan Leffler" <jleffler_at_earthlink.net> wrote in message
news:h3sHb.8655$lo3.5808_at_newsread2.news.pas.earthlink.net...
> Dawn M. Wolthuis wrote:
> > "Jerry Gitomer" <jgitomer_at_erols.com> wrote:
> >>Dawn M. Wolthuis wrote:
> >>>"Joe "Nuke Me Xemu" Foster" <joe_at_bftsi0.UUCP> wrote:
> >>>>"Dawn M. Wolthuis" <dwolt_at_tincat-group.com> wrote:
> >><snip>
> >>>>> Date writes "...MVS fields are ordered left to right (and
> >>>>> so MVS files are certainly not relations, and the system is
> >>>>> certainly not relational)."
> >>>>>
> >>
> >><big snip>
> >>
> >>Allow me to play the role of the fool jumping in where angels
> >>fear to tread.....
> >>
> >>Two points which may clarify RDBMS implementation (as opposed to
> >>theory).
> >>
> >>1. The relationships are imposed externally to the data in the
> >>form of indexes and/or foreign keys. The data itself is
> >>unordered. [...]
> >>
> >>2. Within a table row the physical order of the columns as
> >>stored on disk need not conform to the logical order of the
> >>columns as specified in the CREATE TABLE statement. [...]
> >
> > Yes, this is most helpful. This is PRECISELY my understanding --
> > that deciding to remove the ordering from relational tuples is an
> > implementation issue and not about the logical theory of relations.
> >
> > I work with relations that are mathematical relations and are
> > therefore ordered tuples. The model behind XML documents is also
> > one of ordered tuples. So, if you hear of folks who might sometimes
> > spout that their database model is "more relational" than RDBMS's
> > it sometimes is due to this particular issue.
> >
> > Based on this, it sounds like a response to Date that says that
> > mathematical relations are ORDERED and not unordered tuples so that
> > this particular point is irrelevant (and, in fact, wrong) would be
> > an accurate response, right?
>
>
>
> Accordingly, we propose that users deal, not with relations
> that are domain-ordered, but with relationships which are
> their domain-unordered counterparts.
>
>
>
>
>
Mathematical relations do not rely on attribute order. The physical representation of mathematical relations using written symbols on planar surfaces conventionally uses attribute order for succinctness. Received on Sun Dec 28 2003 - 03:08:08 CST