Subj : Re: Polymorphism sucks [Was: Paradigms which way to go?]
To   : comp.programming,comp.object
From : cb
Date : Thu Sep 22 2005 08:19 am

In article <71n3j19r9fpj6ij591a2pj7vacj2h80cau@4ax.com>,
Chris Sonnack  <Chris@Sonnack.com> wrote:
>topmind writes:
>
>> The term "relational" has nothing to do with keys and their
>> referencing stuff. I used to think it did, but like you now,
>> I was wrong.  You lost this one.
>
>Heh, so you say, but I say Michelle Pfeiffer secretly adores me.
>So, as you see, saying something has no connection with reality.
>
>EVERY resource I checked agrees.  You have yet to produce anything
>other than arm waving to support your point.  If you are right and
>I'm wrong, where's the proof?  Should be easy enough to find.

Let me quote from "An Introduction to Database Systems, Volume 1, Fifth
Edition" by C. J. Date (Addison-Wesley, 1990) - this book, in its various
editions (which include several ones thhat are newer than the one I own,
of course), is often considered _the_ textbook on databases - on page 112,
just at the beginning of section 4.2:

<quote> 

<emphasis> A relational database is a database that is percieved by its
users as a collection of trables (and nothing but tables) </emphasis> .

</quote>

And later on, starting at the bottom of page 115 and continuing onto page 
116:

<quote>

  At this point, the reader may be wondering why relational databases are 
called "relational" anyway. The answer is simple: "Relation" is just a 
mathematical term for a table (to be precise, a table of a cedrtain 
specific kind - details to follow in Chapter 11). [ ... ] In this part of 
the book, in fact, we will generally use the terms "relation" and "table" 
interchangeably, as if they were synonymoss. [ ... ]

  If it is true that a relation is basically just a table, then why not
simply call it a table and have done with it? The answer is that (as
already indicated) we very often do. However, it is worth taking a moment
to understand why the term "realtion" was introducecd in the first place.  
briefly, the explanation is as follows. As already mentioned, relational
systems are based on an underlying set of theoretical ideas knows as the
<emphasis> relational model </emphasis. The principles of the relational
model were originally laid down by one man, Dr. E. F. Codd, at the time a
member of the IBM San Jose Research Laboratory [ ... ] . it was late in
1968 that Codd, a mathematiccian by training, first realized that the
discipline of mathematics could be used to inject some solid principles
and rigor into a field - database management - that, prior tothat time,
was all too deficient in any such qualities. Codd's ideas were first
published in a now classic paper, "A Relational Model of Data for Large
Shared Data Banks") [ ... ] .
  Mow, the relational model as orginally formulated by Codd very 
deliberately made use of certain terms - such as the term "relation" 
itself - that were not familiar in data processing circles at the time, 
even though the concepts in some cases were. The trouble was, many of the 
more familiar terms were very vague and fuzzy. They lacked the precision 
necessary to a formal theory of the kind thaat Codd was proposing. For 
example, consider the term "record". At different times that single term 
can mean either a record <emphasis> instance </emphasis> or a record 
<emphasis> type </emphasis> [ more examples deleted ] . The formal theory 
therefore does not use the term "record"at all; instead, it uses the term 
"tuple" (short for "n-tuple"), which was given a precise definition by 
Codd when he first introduced it. We do not give that definition here; 
for our purposes in the present part of the book, it is sufficient to say 
that the term "tuple" corresponds approximately to the notion of a 
<emphasis> flat record instance </emphasis> (just as the term "relation" 
corresponds approximately to the notion of a table). [ ... ]

</quote>

The Codd paper refered to in the quoted text is:

E. F. Codd. "A Relational Model of Data for Large Shared Data Banks." CACM 
13, No 6 (June 1970). Republished in 'Milestones of Research - Selected 
Papers 1958 - 1982' (CACM 25th Anniversary Issue), CACM 26, No 1 (January 
1983).

In Chapter 11, 'Relation Structure', the book introduces formal definition 
for each term, which I will not quite here; but I will quote form the 
introduction to the chapter, on page 249:

<quote>

[ ... ] We explain each termver  informally here [ ... ] :

* A _relation_ corresponds to what so far in this book we have generally 
  been calling a table.
* A _tuple_ corresponds to a row of such a table and an _attribute_ to a 
  column. The number of tuples is called the _cardinality_ and the number 
  of attributes is called the _degree_.
[ ... ]
</quote>


So, without attempting to validate or invalidate anything else on any side
of any argument, according to what I have quoted above, it should be
fairly clear that the term 'Relational' in 'Relational Database' has
_nothing_ to do with relationships between different tables: The term
'Relation' is instead a different, more precise term for the type of
tables used in Relational databases. So, even a database with only a 
single table, is a relational database.

So, can we please put this particular issue to rest?

Best wishes,

>-- 
>|_ CJSonnack <Chris@Sonnack.com> _____________| How's my programming? |
>|_ http://www.Sonnack.com/ ___________________| Call: 1-800-DEV-NULL  |
>|_____________________________________________|_______________________|

// Christian Brunschen

.