Home -> Usenet -> comp.databases.theory -> Re: algebra equations for Reference and FD constraints

Re: algebra equations for Reference and FD constraints

From: Brian Selzer <brian_at_selzer-software.com>
Date: Thu, 1 Jan 2009 02:05:43 -0500
Message-ID: <bXZ6l.12270$be.10307_at_nlpi061.nbdc.sbc.com> 







"paul c" <toledobythesea_at_oohay.ac> wrote in message 
news:TLQ6l.67470$496.59759_at_newsfe13.iad...


> 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 

> motive.




You're entitled to your opinion--even if it is a product of emotion rather 
than reason.  I'm done here.  Happy New Year!
Received on Thu Jan 01 2009 - 08:05:43 CET












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