Re: Sets and Lists, again

Bob Badour wrote:
> David Cressey wrote:
>
> > "dawn" <dawnwolthuis_at_gmail.com> wrote in message
> > news:1148097777.431200.106670_at_j55g2000cwa.googlegroups.com...
> >
> >>David Cressey wrote:
> >>
> >>>Recently, in a thread on implementing both threads and lists in a
> >>>programming language, the example of lists or sets of Presidents arose.
<snip>
> What if we want to use ordered operations like the above to determine
> the median age at first election? How does the list help us if it is
> ordered by year of first election? If we re-order the list by age, how
> do we put it back to the original order?

The list order is but one possible ordering. You can represent the list as a set ordered by age instead without affecting the logical list. The list is logically equivalent to adding an ordinal attribute in a relation. Working with that relation ordered by something other than what could be implemented in the RM as an ordinal attribute can be done without losing the list order. --dawn Received on Sun May 21 2006 - 01:12:14 CEST