Re: DB2

["Leif Svalgaard" <leif@xxxxxxxx>]

From: Booth Martin <Booth@xxxxxxxxxxxx>

OK, it seems that I still need to say something.
People that want to call their database relational
have said that Codd's rules are too severe, too
academic, too whatever (anything to avoid being
subject to them). And there may be some truth to
that. The main thing about a relational database is
just that, it is "relational". What does that mean?
It is a mathematical term which means a two-
dimensional table which is not homogeneous 
in its rows, ie, the number of rows (unlike the 
number of columns) is not fixed. 
 
 The relation has the following properties: 
Each entry in the table occurs only once, i.e. each row is unique. 
Each column is named 
All values of a given column are of the same type 
Column order is immaterial 
Row order is immaterial 

relations are like sets and share many of the operations that 
can be used with sets. Relational algebra is a mathematical 
formalism for specifying operations on relations. 
The algebra is used to manipulate one or two 
relations as operands to produce a third relation. 

The relational algebra operations are: 
UNION 
INTERSECTION 
DIFFERENCE 
DIVISION 
PRODUCT 
SELECT 
PROJECT 
JOIN 

====

The original S/38 database (still the underpinning for the AS/400
database - and really what we are talking about, because people
keep saying that the DB was relational from the start) permitted
none of this. You used DDS (not even the DB-manipulation 
language itself - one of Codd's rules) to define the database.
The column order matters. Etc, etc.

We are not discussing if DB/2 is relational. It is to a large
degree, but to call the native AS/400 database DB/2 was and
is just a marketing ploy.