Re: two nasty schemata, union types and surrogate keys

From: Roy Hann <specially_at_processed.almost.meat>
Date: Mon, 21 Sep 2009 15:19:29 -0500
Message-ID: <x_udnXz2YKVMQirXnZ2dnUVZ8sudnZ2d_at_pipex.net>



Brian wrote:

> On Sep 21, 10:27 am, Roy Hann <specia..._at_processed.almost.meat> wrote:
>> Brian wrote:
>> > On Sep 21, 3:41 am, Roy Hann <specia..._at_processed.almost.meat> wrote:
>> >> Brian wrote:
>> >> > Databases don't record objects: they record facts [...].  
>>
>> >> Admirably close, but not quite cigar-worthy.  Databases record
>> >> *assertions* of fact.  The assertsions may be sincere and truthful, or
>> >> sincere but false, or deceitful and false.
>>
>> > Whatever.  What is in the database is supposed to be true.  
>>
>> Says who?  
>
> Everyone who advocates the closed world assumption.

The closed world assumption doesn't tell you anything about what is actually in the database; it tells you how you are entitled to manipulate what you find in the database. I hinted at that in my first post when I wrote "All that matters is that we can make the inferences that we should be entitled to make from the assertions."

>> It doesn't need to be true, and it can't be guaranteed to be
>> true, so it is wise to remember that what's in the database is just
>> claims and assertions.  It is completely sufficient that the database is
>> consistent.

> I don't think that it is sufficient.

Well that's too bad, 'cos that's all you can have.

-- 
Roy
Received on Mon Sep 21 2009 - 15:19:29 CDT

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