# Re: Lots of Idiotic Silly Braces?

From: Brian Selzer <brian_at_selzer-software.com>
Date: Fri, 20 Jul 2007 05:54:00 GMT
Message-ID: <Y5Yni.38897\$YL5.701_at_newssvr29.news.prodigy.net>

"paul c" <toledobythesea_at_oohay.ac> wrote in message news: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!)
>

```

r = {{S={{A=3, B=4}, {A=3, B=5}}}, {S={A=3, B=4}}}

r' = {{A=3, B=4}, {A=3, B=5}}

but r' GROUP {A, B} AS S yields either

(1) {{S={{A=3, B=4}}}, {S={{A=3, B=5}}}}

or

(2) {{S={{A=3, B=4}, {A=3, B=5}}}}

For these reasons, I believe that rvas cannot be keys or components of keys--at least not for base relations. Have I overlooked something?

> p Received on Fri Jul 20 2007 - 07:54:00 CEST

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