Re: No exceptions?
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sat, 01 Jul 2006 19:18:04 GMT
Message-ID: <MTzpg.4709$pu3.109666_at_ursa-nb00s0.nbnet.nb.ca>
>>Jon Heggland wrote:
>>
>>>"Every attribute" would also be a superkey (speaking loosely). The empty
>>>set is a subset of every set.
>>
>>I respectfully suggest the confusion caused by your use of key without
>>the 'candidate' qualification demonstrates exactly why we have the term.
>>I suppose irreducible key would do just as well, but for historical
>>reasons, candidate key already means an irreducible key.
Date: Sat, 01 Jul 2006 19:18:04 GMT
Message-ID: <MTzpg.4709$pu3.109666_at_ursa-nb00s0.nbnet.nb.ca>
Jon Heggland wrote:
> Bob Badour wrote: >
>>Jon Heggland wrote:
>>
>>>"Every attribute" would also be a superkey (speaking loosely). The empty
>>>set is a subset of every set.
>>
>>I respectfully suggest the confusion caused by your use of key without
>>the 'candidate' qualification demonstrates exactly why we have the term.
>>I suppose irreducible key would do just as well, but for historical
>>reasons, candidate key already means an irreducible key.
> > I don't think the confusion is on my part. "Key" (as opposed to > "superkey") already implies irreducibility; that's the point of the > superkey/key distinction. A "candidate key" is certainly irreducible > (due to being a key), but "irreducible key" is redundant.
Candidate key, superkey and proper superkey all have different precise
meanings and all of them are keys.
A definition is like a contract for communication and understanding.
When you arbitrarily redefine key to mean candidate key, you breech that
contract and the result of that breech is confusion. Whether the
confusion is on your part, you are nevertheless the cause of the confusion.
By redefining key to mean candidate key, one loses the term that means key. By redefining superkey to mean proper superkey, one loses the term that means superkey.
Your laziness about typing the full names causes confusion and interferes with communication. Received on Sat Jul 01 2006 - 21:18:04 CEST