Re: Interesting article: In the Beginning: An RDBMS history


"dawn" <dawnwolthuis@xxxxxxxxx> wrote in message
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David Cressey wrote:
"x" <x@xxxxxxxxxxxxxx> wrote in message
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I don't think so. I think he was making the distinction between
attributes
specified by name and attributes specified by position.

What is the difference between a "name" and a "position" from a
mathematically point of view ?

I can't speak for Codd on this, and I don't choose to speak for myself.

The only difference is the domain for the function, whether it is a set
of counting numbers or a set of attribute names. If counting numbers,
then there is an obvious order (function), represented as the order of
a tuple.

This is not true.

If the numbers were explictily used as if they were names, in every place
where a specific attribute is specified, your statement would be true.
However, if attributes are expressed in the form of a list, as they are in
mathematics when discussing relations, then the mapping between attributes
and values is based on position in the list.

However, that was not Codd's point.

Codd's point was that users should not have to remember "names" like 23, 24,
25, ...etc. in order to specify attributes in a query.



It amuses me when people make a big deal about there being no order of
the attributes in a relation (which is then not strictly a relation as
Codd pointed out). Given that attributes are specified to the system
in some order (create table...) and output in some order, what do I
care if under the covers it knows a mapping from the counting numbers
to the attribute values or from attribute names to attribute values or
both?

A lot of things amuse you.

In this case, your amusement stems from the fact that you view the text that
represents a create table as being the create table itself. The source code
for a Lisp program is a string of characters. But the actual Lisp program
is a data structure in memory. The Lisp program can have a structure (like
tree structure) that the text source can only express indirectly, through
the use of parentheses.




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