Re: Tarski school influence on Database Theory

Dana petak, 2. listopada 2015. u 22:10:10 UTC+2, korisnik Eric napisao je:
> On 2015-09-29, vldm10 <vldm10_at_yahoo.com> wrote:
> > Dana utorak, 29. rujna 2015. u 19:40:04 UTC+2, korisnik Eric napisao je:
> >> On 2015-09-28, vldm10 <vldm10_at_yahoo.com> wrote:
> >>> Dana ponedjeljak, 28. rujna 2015. u 09:40:04 UTC+2, korisnik Eric napisao je:
> >>>> On 2015-09-25, vldm10 <vldm10_at_yahoo.com> wrote:
> >>>>> On Monday, July 20, 2015 at 16:09:59 PM UTC-7, compdb <compdb_at_hotmail.com> wrote:
> >>>>>> Besides inventing relational algebra, Codd also initiated and championed
> >>>>>> query safety, integrity, normal forms and other issues ...
> >> 8>< --------
> >>>>> Integrity and normal forms. Regarding the normal forms, I must say that
> >>>>> Codd did not invent the "First normal form." ...
> >> 8>< --------
> >>>>> ... records that have a fixed length (that is, they were working with the
> >>>>> first normal form) ...
> >> 8>< --------
> >>>>> So the idea of "First normal form" was performed and analyzed in detail
> >>>>> before Codd. All the advantages and disadvantages of "First Normal Form"
> >>>>> were well analyzed in very complex cases. Note that variable length of
> >>>>> records and entities, we can not apply to relations.
> >>>>>
> >>>>> It is not true that Codd invented the "First normal form". Codd added
> >>>>> "First normal form" to relational model, and he gave the name: "The
> >>>>> first normal form"
> >>>>
> >>>> Fixed length records can not possibly be the same as first normal form
> >>>> since records are about files and first normal form is about relations.
> >>>> However, I can not see at all how they are even in any way similar to
> >>>> first normal form. So what on earth are you talking about?
> >>>
> >>> Have you ever worked with programming languages? If so, have you worked
> >>> with complex data structures by using complex files?
> >>
> >> Yes. And yes. I stand by my first two sentences. So would you please
> >> answer my question.
> >>
> >> Maybe I could amplify the question. What definitions of "first normal
> >> form" and "fixed length records" are you using? I ask for the first
> >> because the concept seems to be widely misunderstood, and it is as well
> >> to be sure that we are talking about exactly the same thing. I ask for
> >> the second because, other than the obvious "all the records always have
> >> the same total length", there is no universal definition of the concept,
> >> and many different ways of using something that conforms to the above
> >> obvious definition.
> >
> > I think you are not well enough, understand this post. I did not write that
> > the file model is in some way similar to relational model.
>
> So, having read the rest of what you say in this post, I now realise
> that what we have is a terminology problem.
 

In my opinion, we do not have a terminology problem, I think the problem is more serious.

> Long ago and far away, when I first started to work with computers, "fixed
> length records" meant that every record in a file was N characters long,
> and was divided into M fields, each of which had a starting position and
> a length and a purpose. This is what I understood you to mean, and of
> course it provides no obvious way to deal with the multiple telephone
> number problem.

The problem with these records is not a variable number of bytes. The problem is so-called "repeating groups". These repeating groups make the corresponding record to be of the variable length. So the main thing here is about the design of database and about constructive elements of this design. These constructions I explained in my post from September 30, 2015. Look at Table A, B and File Customer.

I will also quote C. Date, from his book "An Introduction to Database Systems", sixth edition, 1995, Chapter 4:

" 4. All attributes values are atomic
This last property is, of course, a consequence of the fact that all underlying domains contain values only. We can state the property differently (and very informally) as follows: At every row-and-column position within the table, there is always exactly one value, never a collection of several values. Or equivalently again: Relations do not contain repeating groups. A relation satisfying this condition is said to be normalized, or equivalently to be in first normal form." As you can see, First normal form is related to the repeating groups.

Vladimir Odrljin Received on Mon Oct 05 2015 - 01:14:59 CEST