Re: Sets and Lists, again

From: David Cressey <dcressey_at_verizon.net>
Date: Sun, 21 May 2006 21:33:04 GMT
Message-ID: <k05cg.824$PX3.218@trndny09>

"dawn" <dawnwolthuis_at_gmail.com> wrote in message news:1148165794.460453.268180_at_38g2000cwa.googlegroups.com...
> David Cressey wrote:
> > "dawn" <dawnwolthuis_at_gmail.com> wrote in message
> > news:1148132310.308203.133240_at_g10g2000cwb.googlegroups.com...
> > > David Cressey wrote:
> > > > What's a ripple delete? How is it different from an ordinary
delete?
> > >
> > >
> >

http://www.tincat-group.com/mewsings/2006/01/who-ordered-ripple-delete.html
> > >
> >
> > Can you summarize this?

>

> I was hoping the first few sentences did that, sorry. It is a delete
> that also renumbers or moves up subsequent data. In the case of a
> desired alpha ordering, this is simply a delete. In the case of a list
> or a numbered 1,2...n set (the number being an attribute in a relation,
> for example), removing the 3rd and 4th elements requires renumbering
> all of those after it.

>

> > > > If you have sets, why would you have to "insert at this point"?

>

> In the case of sets that are numbered as above, inserting a new 5th
> element requires that 6...n be renumbered. Have you ever seen the
> design often used with "relational databases" where you leave a range
> of 10 or n numbers on either side of numbered items so that you can
> stick new ones in up to the number of spots reserved? You don't need
> to design that way if using a list where the numbering is behind the
> scenes because the structure is a logical list.
>

If you have lists, you have to renumber every time you retrieve the list, if you desire ordinal numbers to indicate position in the list.

> > [no reply]
> >
> > Again, what does "insert at this point" buy you that insertion into a
set
> > doesn't buy you?
> >
> >
> > > > Why do you need lists for this purpose?
> > >
> > > ? Why do you need lists for the purpose of having list operators?
Can
> > > you rephrase?
> >
> > Sure:
> >
> > What can you do with lists and list operators that you can't do with
sets
> > and set operators?

>

> That is similar to "What can you do with a high level language that you
> could not do with assembler?" Ease of development and maintenance (aka
> cost savings). --dawn

>

That's no explanation at all, Dawn. Your reply presumes that list and list operators are "higher level" than sets and set operators. It seems to me that it's just the reverse. And I think the history of programming languages supports my view. Languages that support lists and list operators predate languages that support sets and set operators. Received on Sun May 21 2006 - 16:33:04 CDT