Re: computational model of transactions

> It is not always the case that if more than one actor is
> updating the same resource, that those updates must be serialized.

I leave that one on your account.

> To illustrate this, ignore the business rules in the above example.

Ignoring business rules is not my idea of a good example. And especially not this kind of example, since I've been a bank programmer for 15 years. I can assure you no one in the bank business would accept the kind of risky manipulations with account balances that you propose.

> The semantics of the update involve modification, not replacement

You obviously see a difference between modification and replacement. I don't. So please explain.

> the operation
> involved, addition, is communitive and associative.

You mean "commuTAtive", of course, and furthermore that's completely irrelevant. As for associativity : it is important to observe that each transaction in this example does exactly one addition with exactly two arguments. So unless you can think of a way for the system to detect that multiple independent transactions are doing such a thing (performing an associative operation), and then replace those multiple independent operations with one single, transaction-surpassing, operation that has the same result, associativity is also irrelevant. If you cannot think of such a way for the system to detect this (I'm in that case), you're stuck with doing multiple additions one-at-a-time, and you're stuck with the fact that for the additions that are executed second and third, one of those arguments should be the result of the former. Therefore it is necessary that the transactions be serialized.  Otherwise it would mean a transaction is allowed to see uncommitted results from another one. Received on Fri Aug 04 2006 - 13:10:17 CEST