Re: Reminder, blatant ad


"dawn" <dawnwolthuis@xxxxxxxxx> wrote in message
news:1138627814.473060.169280@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>
> x wrote:
> > "dawn" <dawnwolthuis@xxxxxxxxx> wrote in message
> > news:1138382966.616817.236670@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> > >
> > > JOG wrote:
> > > > Jan Hidders wrote:
> > > > [snip]
> > > > > > [...] Whenever I mention that I want to
> > > > > > work with such data structures as ordered lists with associated
> > insert
> > > > > > and delete functions, I am informed that I am talking about
> > > > > > representation and that what I want is possible with the data
> > modeled
> > > > > > via the RM and then handled with another product in front of
that.
> > I'm
> > > > > > showing that the RM is all about representation. As soon as you
> > decide
> > > > > > to use another representation, you are moving away from the RM.
> > > > >
> > > > > I don't know who told you that lists are somehow only
representation
> > > > > while sets are not, but that is nonsense. The reason to avoid
lists is
> > > > > far more mundane and practical; it would make the DBMS more
complex
> > and
> > > > > make tasks such as query optimization, concurrency control and
> > integrity
> > > > > maintenance harder. It would also make the theory more complex,
which
> > in
> > > > > the long term usually also translates into practical problems.
> > > >
> > > > I do not agree with this. Conventional ordering (and hence listing)
is
> > > > mathematically impossible in the relational model period, due to the
> > > > Codd's redefinition of RM-relations and the model's closure. Dawn is
> > > > hence correct imo - lists must be interpreted by a process external
to
> > > > the RM, not for the sake of simplicity, or query optimization, but
> > > > rather because the very the nature of that data model precludes
their
> > > > implementation.
> >
> > > I agree (I guess it makes sense that I would agree with you agreeing
> > > with me). While ordering functions (SORT) may be defined on sets,
> > > those are orderings on values. There is no ordering within the
> > > relational structure itself.
> >
> > > Of course you can simulate an ordered list using relations by adding
in
> > > ordering attributes and related functions such as insert & delete.
> > > That could all be done behind the scenes without the programmer
> > > touching the ordering attribute at all. But once the interface to the
> > > user (programmer) has these features, it is no longer an RM interface
> > > because it supports ordered lists. --dawn
> >
> > Talking about the relational model of data and the "list model of data"
> > instead of the relational data model and the "list data model" what is
the
> > advantage of one over the other when modeling the following problems:
> >
> > a) The problem is naturally formulated in terms of named lists of items
and
> > lists operations.
> > How would you implement this with sets and sets operations ?
> >
> > b) The problem is naturally formulated in terms of named sets of items
and
> > set operations.
> > How would you implement this with lists and lists operations ?
> >
> > c) The problem is naturally formulated in terms of sets and lists with
their
> > operations.
> > How would you implement this with lists and lists operations ?
> > How would you implement this with sets and sets operations ?
> >
> > There is a need for an efficient model to support both sets and lists ?

> Yes.
OK.

> > What are the basic operations for combining lists and sets ?

> The ones that come with any general purpose programming language.
Can you make a list or a set with them and post it ?

> >
> > Where do we stop ?

> I'm good with programming languages as a "stopping point" building up
> from there to higher levels with libraries of code.

Well, the programmig languages are many. :-)
What programming languages are you refering to ?
The future ones ?

> > Why not asking for a model to support all mathematics ?

> Again, I'm good with programming languages and libraries thereof.

A variable SET of variable LISTs of symbols and a variable SET of variable
LISTs of substitution rules LISTed in some order is what you propose ?
Or the other way around ?
Can you make such a thing declarative (specifying the data, not the process
of getting the data) ?


.

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