Re: SQL, related records (quotes)
Date: Sun, 26 Jun 2005 11:38:13 GMT
"Stefan Rybacki" <stefan.rybacki_at_gmx.net> wrote in message
> Dan Guntermann wrote:
>> But alas, not many implementations allow for assertions of antisymmetry,
>> though it could be done with a trigger. This approach would enforce the
>> condition that
>> for all (child, parent) relationships that are members of hierarchies,
>> there does not exist a tuple of (parent, child). It also has the
>> limiting factor of disallowing single node hierarchies.
> You meant non-symmetry since anti-symmetry says: you can have (child,
> parent) and (parent, child) at the same time execept parent=child
Deesn't non-symmetry simply mean there exists a tuple <child X, parent Y> in
hierarchies such that there is no corresponding tuple <child Y, parent X> in
hierarchies? This isn't the same as a universal quantifier.
No. I still think anti-symmetry in conjunction with non-reflexive holds
here. Does the following meet the definition of anti-symmetry that you
No. I still think anti-symmetry in conjunction with non-reflexive holds here. Does the following meet the definition of anti-symmetry that you state above?
child parent 6 3 3 6
If it doesn't, then it makes sense that the DBMS reject such a condition. Obviously 6 does not equal 3.
> Just mentioned ;) (I know antisymmetry works here since you said you don't
> allow reflexive tupels)
Dan Received on Sun Jun 26 2005 - 13:38:13 CEST