Re: Tarski school influence on Database Theory
Date: Mon, 5 Oct 2015 18:06:07 +0200
On 2015-10-04, vldm10 <vldm10_at_yahoo.com> wrote:
> 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.
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 lbryReceived on Mon Oct 05 2015 - 18:06:07 CEST