# Re: separation of church and state?

From: paul c <toledobythesea_at_ooyah.ac>
Date: Sun, 07 Oct 2007 20:24:52 GMT
Message-ID: <ogbOi.1580\$Da.218_at_pd7urf1no>

```>> Could be.  Maybe one of Date's meanings is that no system that supports
>> both ordering and some relational algebra is purely relational, even if
>> the "pure" relational part of it could be isolated in some way from the
>> rest!  If so, calling the paragraph "doctrinaire" might be a bit of a slur.
```

>
> In order theory, an ordered set is a pair, consisting of a set and an
> order relation on that set. It's not a list or anything like that.
> The question of data structures only comes up when (in
> implementation land) we want to do the computation of putting
> the elements in some order. What that looks like is a design
> decision, and I don't see any reason why it can't look like a
> relation, at some level at least. In other words, it could be a
> relation {position, element} in the case of a total order, or
> {position, {element}} in a preorder. (It's not obvious what
> it should be for a partial order.)
>
> My sense is that Date's ideas about the solution space to
> this problem have been somewhat artificially constrained
> as a response to what SQL did.
>
>
> Marshall
>

Just shooting my mouth off about somebody I don't know, but regarding Date's thoughts being limited by products, I'd say if anything his writings about relations are more influenced by the adhoc methods of thirty or more years ago. I remember being ordered to attend many tutorials about IMS and the Cullinane, Cincom stuff, in fact they were actually brainwashing sessions about what were really single-application solutions.

I don't agree with that stuff anymore, haven't for at least twenty years, but some of the "old order" (sorry for the pun), eg., adhoc sorts, still seems reasonable to me for most purposes, even though they depend on various arbitrary representations, such as fixed point decimals and so on. For me the possibility of using relations to describe how a sort is to operate doesn't come up much as a solution to an application problem. Actually, I wouldn't know how to do it either but I'd grant that exploring it might lead to some good insights that might be applied to other problems. Received on Sun Oct 07 2007 - 22:24:52 CEST

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