Re: Tarski school influence on Database Theory

From: Eric <>
Date: Mon, 5 Oct 2015 18:06:07 +0200
Message-ID: <>

On 2015-10-04, vldm10 <> wrote:
> Dana petak, 2. listopada 2015. u 22:10:10 UTC+2, korisnik Eric napisao je:
>> On 2015-09-29, vldm10 <> wrote:
>>> Dana utorak, 29. rujna 2015. u 19:40:04 UTC+2, korisnik Eric napisao je:
>>>> On 2015-09-28, vldm10 <> wrote:
>>>>> Dana ponedjeljak, 28. rujna 2015. u 09:40:04 UTC+2, korisnik Eric napisao je:
>>>>>> On 2015-09-25, vldm10 <> wrote:
>>>>>>> On Monday, July 20, 2015 at 16:09:59 PM UTC-7, compdb <> 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.

Yes, first normal form is related to repeating groups. But repeating groups are not at all related to what I have always believed to be the important distinction between fixed length and variable length records. As I said, you can have a repeating group in a fixed length record, and there is no need to have one in a variable length record. You and I are using the phrases "fixed length" and "variable length" to mean different things, so yes it is a terminology problem.

Now I believe I do understand what you mean, but I don't believe that it supports your claim that Codd's "normalisation" was merely a naming of something already done. Neither the context nor the justification are the same so there is only a similarity which proves nothing.


ms fnd in a lbry
Received on Mon Oct 05 2015 - 18:06:07 CEST

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