Re: atomic
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Fri, 02 Nov 2007 18:19:04 -0300
Message-ID: <472b944c$0$14867$9a566e8b_at_news.aliant.net>
>
> ...
>
>
>
> If we mean salaries for one employee, eg., a single attribute relations
> like:
>
> KnownSalariesForJoe
> ___________________
>
> {10,000, 20,000},
>
> how could we make sense of:
>
> KnownSalariesForJoe
> ___________________
>
> {}
>
> ?
>
> eg., if the set of known salaries for "Joe" is empty, a dbms that
> supports RVA's can record this second relation, but couldn't we just as
> well have an empty value for it:
>
> KnownSalariesForJoe
> ___________________
>
>
> so I wonder: why allow the predicate to require a set in the first place?
>
> One argument for why might be that the predicate has been agreed to by
> all users (after a million dollars was spent assiduously gathering
> requirements). But when it comes to unnecessary requirements I don't
> care many how many users agree!
>
> If we mean "known salaries for each employee", I think that phrase
> presumes that we can identify each employee which means that Codd's
> "normalization" method in his 1970 paper applies, which means in turn (I
> think) that we don't need RVA's for this relation, so for me the
> question of an empty RVA doesn't "need" to come up.
Date: Fri, 02 Nov 2007 18:19:04 -0300
Message-ID: <472b944c$0$14867$9a566e8b_at_news.aliant.net>
paul c wrote:
>> paul c wrote:
>
> ...
>
>>> >>> For example? >> >> >> The set of known salaries for an employee.
>
>
> If we mean salaries for one employee, eg., a single attribute relations
> like:
>
> KnownSalariesForJoe
> ___________________
>
> {10,000, 20,000},
>
> how could we make sense of:
>
> KnownSalariesForJoe
> ___________________
>
> {}
>
> ?
>
> eg., if the set of known salaries for "Joe" is empty, a dbms that
> supports RVA's can record this second relation, but couldn't we just as
> well have an empty value for it:
>
> KnownSalariesForJoe
> ___________________
>
>
> so I wonder: why allow the predicate to require a set in the first place?
>
> One argument for why might be that the predicate has been agreed to by
> all users (after a million dollars was spent assiduously gathering
> requirements). But when it comes to unnecessary requirements I don't
> care many how many users agree!
>
> If we mean "known salaries for each employee", I think that phrase
> presumes that we can identify each employee which means that Codd's
> "normalization" method in his 1970 paper applies, which means in turn (I
> think) that we don't need RVA's for this relation, so for me the
> question of an empty RVA doesn't "need" to come up.
We never "need" RVA's.
> (I should say that I'd guess Bob B among others here might guess that
> I'm talking towards my usual recurring them, to do with RVA's and
> recursion, the possible importance of which I admit I haven't been able
> to express in concise terms.)
Recursive type declarations work just fine without any problems.
Recursive value declarations would not. You seem to keep thinking
recursive type declarations have the same problems as recursive value
declarations. They don't.
R = { A int, B typeof R } -- works