Re: cdt glossary 0.1.1 [Transaction]
Date: Fri, 20 Apr 2007 13:22:07 GMT
Message-ID: <383Wh.100591$DE1.26701_at_pd7urf2no>
Brian Selzer wrote:
> "paul c" <toledobythesea_at_oohay.ac> wrote in message
> news:x6SVh.98742$DE1.19705_at_pd7urf2no...
>
>>mAsterdam wrote: >> >>>paul c wrote:
>
> [snip]
>
>
>>I wasn't suggesting it did. As far as I know, "order of work" is not a >>relational issue, nor is a transaction a relational concept any more than >>invoices are. Wondering why they aren't part of RT is like asking why the >>RM isn't based on a state machine. >>
>
>
> So what would you call something that transforms one database state into
> another? In 1970, Codd called them "state-changing transactions."
> ...
Codd subscribed to the idea of a data sub-language. I think whenever he
used terms such as "states" and "transactions", he was talking about a
programming environment, not the RM.
...
> I think that if a transaction contains more than one operation, then the
> order in which each operation is evaluated is critical. 2 + 3 * 5 = 17, not
> 25.
>
> After the following transaction,
>
> UPDATE r SET x = x + 5 WHERE k = 22,
> UPDATE r SET x = x * 4 WHERE k = 22
> ...
> Is the result (x + 5) * 4 or (x * 4) + 5? Or is it x * 4, which is what
> D&D's multiple assignment would produce?
> ...
> Do you limit a transaction so that only one transformation can occur per
> relation? Per tuple? Per attribute value?
> ...
Any concept of a database that has two different values at the same time is beyond me.
> Should all constraints be checked after each operation? Only some? Or
> should they all be deferred until the end? I mention this because the
> result of one operation may leave the database in an inconsistent state,
> making any subsequent operations suspect.
> ...
Any dbms that allows a programmer to introduce an inconsistency should be recalled.
> If it were possible to convert a group of statements into a single
> operation, then there would be no need for order, there would only be one
> transformation per relation, per tuple and per attribute value, and
> constraints would only need to be checked once. Alas, this capability is
> not available in any commercial system that I know of, and even D doesn't
> doesn't support it.
> ...
So what? (Most of IT is mistaken. People usually prefer to re-invent old wheels.)
p Received on Fri Apr 20 2007 - 15:22:07 CEST