Re: Lots of Idiotic Silly Braces?
Date: Tue, 17 Jul 2007 02:31:45 GMT
Message-ID: <lSVmi.123823$xq1.100625_at_pd7urf1no>
Bob Badour wrote:
> paul c wrote:
>
>> Bob Badour wrote:
>>
>>> paul c wrote:
>>
>>
>> ...
>>
>>>> The predicate somebody intends by this grouping could be "Shipment S
>>>> included the set of parts {P}". If we then ask "what combinations
>>>> of parts have been shipped?", a knee-jerk reation might be to
>>>> project away the S attribute:
>>>>
>>>> {P}:
>>>> {3,4}
>>>> {3}
>>>
>>>
>>>
>>>
>>> This represents it as one table.
>>> ...
>>
>>
>> I guess I was using the word "table" pretty casually. I'm fairly sure
>> Codd didn't mention it much, talking rather of "normalization", and
>> maybe I shouldn't suggest to compare the two, eg., he said:
>>
>> "Normalization proceeds as follows. Starting with the relation
>> at the top of the tree, take its primary key and expand
>> each of the immediately subordinate relations by
>> inserting this primary key domain or domain combination.
>> The primary key of each expanded relation consists of the
>> primary key before expansion augmented by the primary
>> key copied down from the parent relation. Now, strike out
>> from the parent relation all nonsimple domains, remove the
>> top node of the tree, and repeat the same sequence of
>> operations on each remaining subtree."
>>
>> If I follow this literally, I suppose the fact that I can't "strike
>> out ... all nonsimple domains", means that I am left with what I
>> started with, namely a relation, you are saying that the table and
>> relation in this case are one and the same, and you might say I am
>> grasping at graphical representation that is an impossible
>> over-simplification!
>
>
> Because the primary key is {P}, if you follow the instructions
> literally, you will normalize the relation to:
>
> {P} P
> ==== ----
> {3,4} 3
> {3,4} 4
> {3} 3
>
> I do not believe his instructions anticipated a relation valued primary
> key.
I didn't read it that way, but I guess the paragraph does leave it a little open to that interpretation. Anyway, thanks, I suspect you are right about it not covering rva's that are keys. I imagine that if he had tried to cover every last detail, that paper might not have had the impact it did, but what do I know? (don't answer that!)
p Received on Tue Jul 17 2007 - 04:31:45 CEST