Re: algebra equations for Reference and FD constraints
Date: Thu, 1 Jan 2009 02:05:43 -0500
"paul c" <toledobythesea_at_oohay.ac> wrote in message
> Brian Selzer wrote:
>> Codd wasn't being sloppy. It does not logically mean that time values
>> are involved: it means that the instantaneous state of the data bank at
>> one arbitrary point in time can be a different collection of relations
>> than that for the instantaneous state of the data bank at another
>> arbitrary point in time.
> In that case better to call them a time-varying collection.
>> ... Database updates are indeed a relational model concept even though
>> neither the algebra nor the calculus are sufficient to express them..
> Try and tell that to a computer. Go on, I dare you. When that doesn't
> work try and show us a formal definition of update that doesn't depend on
> set difference and union. Remember 'FORMAL', not Oracle or SQL
> wishy-washy prose.
>> I don't agree with Date's characterization, nor with his conception that
>> a database is a collection of relvars. There are several reasons, not
>> the least of which is that its intended interpretation relies upon the
>> false assumption that key values rigidly designate individuals in the
>> universe of discourse, but most importantly it is that Date asserts that
>> relational assignment is a primitve operation when it is clear that
>> information is lost when UPDATE is translated into assignment. Using the
>> primitives insert, update and delete, it is possible to describe
>> completely--down to the attribute value--what is different between
>> successive databases. ...
> That's a load of bull, along with the stuff I snipped. Eg., Date hardly
> ever talks about keys except in the context of data structure/constraints
> or when he's making fun of ER models. You appear to have a pathological
> mania for expanding the vocabulary of every problem so far as to make it
> insoluble (even farther, don't ask me why). When normal people find it
> enough to talk of values, you want to include 'states', when it's legit to
> talk of 'primitive' algebraic ops, you abscond with the word and attach it
> to non-logical, interpretive motives. Airy-fairy but not productive. I'll
> bet you're a consultant. At least when Celko pops off here, we know his
Received on Thu Jan 01 2009 - 08:05:43 CET