Re: does a table always need a PK?

Hello there,

"Heikki Tuuri" <Heikki.Tuuri_at_innodb.com> wrote in message news:<Xr63b.703$n62.374_at_read3.inet.fi>...
> yes, you understood what I meant.
Good-o.

> It is rather easy to formalize that the
> query language must be able to perform the operations of the relational
> algebra, since the relational algebra is a simple mathematical system.
So the immediate question that springs to mind is, so why did DBMS vendors do SQL instead ?

> But a DBMS is a kind of operating system, too. And it is hard to define
> formally what required concurrency, backup, sysadmin, communications, etc.
> handling capabilities are for a program to be called a DBMS.
>
Indeed. Which is why I had issues with the initial answer, requesting something which I suspected we both knew didn't currently exist and would be non-trivial to formulate. I would ask, though, why we would be asking for a mathematical def'n of something about which mathematics currently has little or nothing to say ? (Or has someone produced a mathematical model of a tape drive, how to write to it, and what a backup to it means, for example ?) Or put more simply, do all formal def'ns have to be mathematical def'ns, or are there some problems for which we have to descend to natural language (with all that entails) whether we like it or not ?

However, even without mathematical def'ns, we have operating systems, and DBMSs. A mathematical def'n may well improve our understanding of DBMSs further; could I then make a product request that a mathematical def'n be formulated and implemented as MySql 6 ? :)

> About the horse: if we genetically engineer a horse and add DNA from a frog,
> at what point does the creature transform from a horse to a froghorse?
>
An interesting question - which leads to other interesting questions about how pure horse DNA has to be at any given time to qualify as a horse (e.g. are only thoroughbred racehorses with provable ancestry really horses ?) Not being a geneticist I'm not going there - I know I don't know enough about that to hold a reasonable discussion on it !

• Tony