Re: Ping: dawn, some mvl questions

mAsterdam wrote:
> Keith H Duggar wrote:
> > If my grandmother hands me a recipe written on a piece
> > of paper and I type it into emacs to store as a text
> > file, do I lose information?
>
> Retorical, but I'll answer any, just to be specific:
> Yes. Historians may come up with more, but here is some:
> Her handwriting. Some of the layout. The age of the
> paper. Dents from writings on other papers.

Precisely! There is a wealth of PHYSICAL information lost whenever we change PHYSICAL representation. Hence the great importance of developing a LOGICAL model and to make all information DEEMED important EXPLICIT rather than IMPLICIT.

> However, if she wrote it down in a particular order, not
> based on the content, that order is exactly the
> information you lose by sorting the ingredients by
> quantity. You will never be able to reconstruct the source
> order if you don't keep it e.g. by adding the original
> line numbers in your plain text file.

The key here is "not based on the content". That is the problem we must avoid. For by content you must mean LOGICAL content. Any information we wish to preserve across PHYSICAL representations MUST be made part of the logical content.

> > If you want to use a logical data model that assumes
> > some built-in implicit (physical?) order is meaningful
> > nothing is stopping you. Though it is certainly not
> > necessary to do so (the RM for example) and many have
> > argued quite reasonably that such order dependence is a
> > bad idea.
>
> So let's lose the order? I don't think that is wise
> always.

No I think you are missing the point or obscuring it. The argument was against IMPLICIT or PHYSICAL order not order of any kind. To make sure other points are not lost key words in what I wrote here and before include: PHYSICAL, LOGICAL, IMPLICIT, EXPLICIT, DEEMED, AGREED, and COMMON.

> I have only seen a priori dismissal of meaning of order,
> coerced by the toolkit. Nails and hammers.

Strange. I'm fairly new to most of these topics, however, even in my short study here I have seen well reasoned arguments against IMPLICIT and PHYSICAL order. For example see Codd 1970 1.2.1 for argument against depending on physical order and starting in 1.3 for arguments against dependence on implicit domain oder. Hence his proposal to deal with domain-unordered relations. I think dbdebunk has a paper (maybe several) on the topic. These were certainly NOT "a priori dismissal"s. Really, you can find a number of well reasoned arguments yourself if you try.

> Maybe you can reiterate the reasonable arguments.

I'm sorry no. First I don't feel qualified at the moment, second there is even a current topic in this group discussing list vs set, and third I'm sure you can easily find more references yourself in addition to Codd 1970.

Finally, I really don't understand the repeated "nails and hammers" analogy in this context. Are you trying to say "if all one has is LOGIC everything is LOGICAL"? :-)

• Keith ---