dawn wrote:
>
> Outside of the issue of how coupled a logical model is to the physical
> model, I see no harm in numbering the attributes provided you also name
> them.
It also makes the theory more complicated than necessary. What if we
take the join of two relations, what is then the order of the
attributes in the resulting table? How do you define this such that a
join is still commutative? This is rather crucial for quey
optimization. And what about unions? Are they allowed already if the
set of attributes is the same, or does their order also have to be the
same? If the orders are allowed to differ, how is then the order in the
result of the union defined in such a way that we keep the usual
algebraic identies?
Received on Fri Apr 07 2006 - 03:50:12 CDT
