Re: Tarski school influence on Database Theory
Date: Tue, 29 Sep 2015 15:11:25 -0700 (PDT)
Message-ID: <22b35370-9a32-4401-b436-a81977042705_at_googlegroups.com>
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.
>
> Thankyou.
>
> Eric
> --
> ms fnd in a lbry
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.
I wrote the following:
1. Codd has applied the idea and the procedure that was used in the file
model.
2. This idea and the procedure have been used for many years, before Codd.
In some programming languages there are commands that enable you to work
with variable records. There is also the possibility of switching from a
record with variable length to the record with the fixed length, in
accordance with the mentioned idea and procedure.
3. I wrote that a file with records of fixed length, correspond to a
relation that is in first normal form.
4. This idea and the existing procedure were applied in the relational model
by Codd. Codd was only invented the name for this procedure. He named this
as the "First normal form.". However, as I have already said this idea and
this procedure were invented before Codd.
I'll try to explain this procedure on the simple example from the article, taken from Wikipadia. The title of this article from Wikipedia is "First normal form", the address of the text from the web is: https://en.wikipedia.org/wiki/First_normal_form
Example
TABLE A
Customer
----------------------------------------------------------------------------
CustomerID First Name Surname Telephon Number
----------------------------------------------------------------------------
123 Robert Ingram 555-861-2025
----------------------------------------------------------------------------
456 Jane Wright 555-403-1659
555-776-4100
----------------------------------------------------------------------------
789 Maria Fernandez 555-808-9633
----------------------------------------------------------------------------
In this example, attention is focused on attribute Telephone number for "Jane Wright."
Next step is TABLE B:
TABLE B Now here: In the first normal form, the previous table can be represented in the following way.
Customer
----------------------------------------------------------------------------
CustomerID First Name Surname Telephon Number
----------------------------------------------------------------------------
123 Robert Ingram 555-861-2025
----------------------------------------------------------------------------
456 Jane Wright 555-403-1659
456 Jane Wright 555-776-4100
----------------------------------------------------------------------------
789 Maria Fernandez 555-808-9633
----------------------------------------------------------------------------
============================================================
Note that in Table A, column "Telephone Number" was presented in a strange
way, because this is something you can not write in any data model. So this
is not normal presentation of data, which can not be presented in any of the
existing software.
I think here on "vertical presentation of values" from telephone number. TABLE B also can not be presented in an existing software, because the key 456 is a double key.
In contrast to relational model, this can be represented in the model file:
FILE Customer
CustomerID First Name Surname Telephon Number
123 Robert Ingram 555-861-2025 ---------------------------------------------------------------------------- 456 Jane Wright 555-403-1659 555-776-4100 --------------------------------------------------------------------------- 789 Maria Fernandez 555-808-9633 ----------------------------------------------------------------------------
In this file, the record with the key 456 is a typical variable record . One person can have 1 or 2 or 3 or ... or n telphones. This file with variable record can be broken down into two files. So in file data model, many professionals were applied decomposition of the files and they were brought into first normal form. As I said in my first post, some project managers insisted, in pre-Codd time, that the data structures should be in the form of a fixed record that is in First normal form.
Note that in variable part from the file we can set the values of keys.
If these are the keys that are from current file, then you can walk through
your file, in the way you specify. This "walking" through the existing file,
can be logically determined. If these keys are from another file, then you
have a connection with the other file.
If these keys are from another four files, then the variable portion
connects four different data structures. With this small example I want to
emphasize the great possibilities which has the variable record.
In fact in this story about the keys and files with repeating groups we can
see that this story becoming story about build a database by using files.
At the beginning of this article from Wikipedia, about First normal form,
the author determines some basics.
He wrote the following: First normal form enforces these criteria:
- Eliminate repeating groups in individual tables. - Create a separate table for each set of related data. - Identify each set of related data with a primary keyNote that repeating groups is synonym for variable length records. Further in this article, in section "Further reading" you can find: " Kent, W. (1983) A Simple Guide to Five Normal Forms in Relational Database Theory" Here in section "First normal form" you can find the following text: "First normal form [1] deals with the "shape" of a record type." This is record of the fixed length. As you can see variable and fixed length of record are terms which were used in RM literature.
In section "Atomicity", author of the web article write about Codd's idea about First normal form. He wrote: Edgar F. Codd's definition of 1NF makes reference to the concept of 'atomicity'. Codd states that the "values in the domains on which each relation is defined are required to be atomic with respect to the DBMS."
In same section the author of the article wrote: First normal form, as defined by Chris Date, permits relation-valued attributes (tables within tables). Date argues that relation-valued attributes, by means of which a field within a table can contain a table, are useful in rare cases.
In my opinion Codd i Date didn't completely understand Frege's theory. You can see Frege's "relations" in my post of September 24, 2013, in thread "Sensible and NonsenSQL Aspects of the NoSQL Hoopla". In this post you can notice, that Frege presented some kind of "nested predicates". In this post you can see exactly what Frege called relations. My approach in the construction of the database is different from Codd's. However you asked me, what is in my opinion First normal form. If we are talking in simplified terms then First normal form is Codd's first step in the process of building a relational database.
Vladimir Odrljin Received on Wed Sep 30 2015 - 00:11:25 CEST