Re: Sets and Lists, again
Date: 22 May 2006 16:42:22 -0700
Message-ID: <1148341342.580083.39780_at_y43g2000cwc.googlegroups.com>
David Cressey wrote:
> "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.
I'm working at the logical level where an index holds the ordinal position. This position can be selected just as any attribute (derived or otherwise). There is no renumbering required.
>> > >
> > > [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.
For the problem domains I have worked with, nothing could be done with one that could not be done with the other data model. When a list is logically modeled as a set, more work is required, however. So for the typical business data processing application, the RM is simply a more primitive means of modeling a list. It is similar to working with assembler when one could use a higher level language for the average use. Do you still disagree with that assessment? --dawn Received on Tue May 23 2006 - 01:42:22 CEST