paul c wrote:
> 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!)
I would simply note that "genius does not imply perfect." The paper is a
work of genius regardless.
Received on Mon Jul 16 2007 - 21:49:07 CDT
