Re: RA with MV attributes

From: paul c <toledobythesea_at_oohay.ac>
Date: Wed, 17 Jan 2007 14:27:19 GMT
Message-ID: <bnqrh.674673$1T2.569295@pd7urf2no>

Bob Badour wrote:

> Jon Heggland wrote:
> 

>> David wrote:
>>
>>> Example
>>>
>>> r1(Names,Cars)
>>> bill, car1,car2,car4
>>> john,fred car3
>>>
>>> r2(Cars,Colours)
>>> car1,car3,car4 red
>>> car2 green
>>>
>>> r1 |X| r2 (Names,Cars,Colours)
>>> bill car1,car4 red
>>> bill car2 green
>>> john,fred car3 red
>>> john,fred green
>>>
>>> [...]
>>> For example the
>>> last tuple of r1 |X| r2 above doesn’t imply that John and Fred
>>> don’t own any cars.
>>
>>
>>
>> So what exactly does that last tuple mean?

> 
> 
> And what would happen if we replaced (car1,car3,car4)<->(red) with 
> (car1,car3,car4)<->(red,blue) in r2 ?
> ...

Just curious, what does the symbol <-> stand for here?

p Received on Wed Jan 17 2007 - 08:27:19 CST