Talk:Armstrong's axioms
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the sentence "Where XZ means the collection of all attributes in X and Z." is ambiguous, the fact its union should be made explicit -- James Hogan 08:44, 14 June 2007 (UTC)
You are right, James Hogan, it is not understood whether I mean the union or the intersection of two sets. I fixed it. Paolo Serafino 17:57, 15 June 2007 (UTC)
According to our lecturer at the university rule 1 should not be applied on functional dependencies, but on attributes of the relationship itself. This is not mentioned in this article. —Preceding unsigned comment added by 83.180.9.80 (talk) 18:08, 13 November 2008 (UTC)
Pseudo-transitivity[edit]
I've been staring at the pseudo-transitivity rule for some time now and I can't make out how to prove it from the three fundamental axioms. On the other hand, proving AC -> D is straightforward. Could someone comment on this? Aednichols (talk) 20:38, 7 December 2012 (UTC)
Aednichols ^ I think it follows from combining the Axiom of augmentation and the Axiom of transitivity. If we have been given A -> B, then augmentation allows us to say: AC -> BC. If we have also been given that BC -> D then transitivity allows us to shorten AC -> BC and BC -> D to AC -> D Roland Bouman (talk) 13:15, 7 April 2015 (UTC)
Why does the piece on Pseudo-transitivity use A, B, C and D? If A, B, C and D are all subsets of attributes then this should be defined. And it would be even better if all rules were re-written using A, B and C (and D where necessary) Roland Bouman (talk) 13:08, 7 April 2015 (UTC)
Unclear[edit]
The article assumes that the reader knows what the symbols mean. The "C underscore" and arrow symbols should be explained. — Preceding unsigned comment added by ThomasMcA2 (talk • contribs) 23:15, 19 March 2013 (UTC)