Re: repeating groups

From: dawn <dawnwolthuis_at_gmail.com>
Date: 19 Feb 2006 09:52:26 -0800

David Cressey wrote:
> "mAsterdam" <mAsterdam_at_vrijdag.org> wrote in message
> news:43f85250\$0\$11077\$e4fe514c_at_news.xs4all.nl...
> > Marshall Spight wrote:
> >
> > > ... Lists are essential; sets are
> > > essential; I am not willing to admire a language that doesn't make
> > > both of them first class. I am not convinced there is any other
> > > structure that we need to give such importance to. And lists and
> > > sets need to interoperate. Hence we have to have the unified
> > > algebra.
> > >
> > > job is remarkably easy. What is remarkably hard is to actually
> > > do a good job.
> >
> > Suggested steps:
> >
> > 0. (preliminary): device a unified notation, specifically for
> > this purpose
> > 1. Formulate the Spight list algebra :-)
> > 2. Reformulate the relational algebra
> > 3. Merge
> > 4. Pizza!

```>
```

> Excellent! Maybe at that time someone will finally tell me whether a pizza
> with onions and mushrooms is or is not the same as a pizza with mushrooms
> and onions. I recall asking something like this about two years ago, in
> here, and not getting a firm answer.

Taking the question seriously...they are not the same. For people who wish to remove all mushrooms, they are easier to remove if the mushrooms are placed on last. On the other hand, if someone requests the two toppings, the order they list them has no bearing on the order they are added. The pizza chef almost always determines the ordering.

> What I really meant by that somewhat whimsical question is whether lists and
> sets have to be implemented and described separately, or not. I'm glad to
> see the discussion coming around.

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