Re: Stored fields ordered left to right
From: Dawn M. Wolthuis <dwolt_at_tincat-group.com>
Date: Tue, 13 Jan 2004 08:13:24 -0600
Message-ID: <bu0ue8$nmj$1_at_news.netins.net>
> Marshall Spight <mspight_at_dnai.com> schrieb:
> >> A modelling tool should deliver a straightforward mapping between the
> >> parts of the model and the parts of the system we're modeling. With
> >> relations it is easy to make such a mapping by treating relations as
> >> logical predicates: "so-and-so LIVES AT such-and-such-a-place". I don't
> >> see how such a mapping would work in general for functions.
> >
> > It's the *exact* *same* *mapping.* The only difference is that you
> > are limited to a single key.
>
> It can't be the same mapping, as proven by example; the 3-part predicate
> "person LIVES AT place DURING time period" has an obvious mapping to the
> columns of a relation. To which parts of this predicate do the DOMAIN
> and RANGE of a function correspond?
Date: Tue, 13 Jan 2004 08:13:24 -0600
Message-ID: <bu0ue8$nmj$1_at_news.netins.net>
"Adrian Kubala" <adrian_at_sixfingeredman.net> wrote in message news:slrnc0794s.3b7.adrian_at_sixfingeredman.net...
> Marshall Spight <mspight_at_dnai.com> schrieb:
> >> A modelling tool should deliver a straightforward mapping between the
> >> parts of the model and the parts of the system we're modeling. With
> >> relations it is easy to make such a mapping by treating relations as
> >> logical predicates: "so-and-so LIVES AT such-and-such-a-place". I don't
> >> see how such a mapping would work in general for functions.
> >
> > It's the *exact* *same* *mapping.* The only difference is that you
> > are limited to a single key.
>
> It can't be the same mapping, as proven by example; the 3-part predicate
> "person LIVES AT place DURING time period" has an obvious mapping to the
> columns of a relation. To which parts of this predicate do the DOMAIN
> and RANGE of a function correspond?
A predicate would look like this:
person IDENTIFIED BY id LIVES AT place DURING time period
I'll name the function using the plural rather than singular (for reasons I won't go into and of course there are differences of opinion on this) and the function is
STUDENT-SCHEDULE(student,term) = { (courses, days of week, start time, end
time)* }
using the XML notation of * to indicate a repeating group, i.e. nested
table.
Thank you gentlemen, I think I have the information I need on this one. Cheers! --dawn Received on Tue Jan 13 2004 - 15:13:24 CET