Re: Objects and Relations

From: Joe Thurbon <usenet_at_thurbon.com>
Date: Thu, 15 Feb 2007 22:14:27 GMT
Message-ID: <7X4Bh.1630$4c6.1167@news-server.bigpond.net.au>

Bob Badour wrote:
> Joe Thurbon wrote:

>>
>> I guess I was thinking along these lines. Say, for example, social 
>> security fraud. When you see some tuples in some PEOPLE relation, with 
>> a primary key SSN.
>>
>> Person: {<SSN:12345, Name:"Fred">, <SSN:23456, Name:"Bill">}
>>
>> it is safe to assume that
>>
>> - there is an entity we are modelling, call him entity_fred,
>>      with a name "Fred", and
>>      an SSN 1234.
>>      No other entity exists with a SSN 12345.
>>
>> - there is an entiry we are modelling, call him entity_bill,
>>      with a name "Bill" and,
>>      an SSN 2345.
>>      No other entity exists with a SSN 12345.
>>
>> However, the relation, taken alone, does NOT mean that the entity_fred 
>> and entity_bill are distinct entities.

>
> Person is just a name for a predicate. Whether and how it describes
> anything in 'the real world' is part of the external predicate.

"External Predicate." I was not aware of that term. A quick google has helped me clear this confusion up.

Thanks.

> The dbms
> neither knows nor cares about the meaning of the word 'Person'. One
> could replace the name 'Person' with 'Hornswoggle' or 'x' and the dbms
> wouldn't care or notice. Hornswoggle would work exactly like Person.
>

Yes, I was aware of this part.

Cheers,
Joe Received on Thu Feb 15 2007 - 16:14:27 CST