I just checked C J DATE , where in chapter 11 , page 339 it lists a rule called composition , if a->b , c->d then ac->bd , so that answers part of my query but am curious as to why it says otherwise in navathe .
Functional dependency
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30-11-2021 - |
Question
if x->a and y-> b
then
from x->a == xy-->ay [ir2] xy-->a [ir4]
from y->b == xy-->xb [ir2] xy-->b [ir4]
therefore xy-->ab [ir5]
But elmasri navathe says , x-->a and y-->b DOES NOT IMPLY xy-->ab i am just starting with functional dependency , so could some one point out what i am missing ?
Solution 2
OTHER TIPS
Although my knowledge on functional dependencies is not complete at all, I do not see any mistakes in your way of thoughs.
Could you provide an excerpt of the text?
I found a copy of the book I guess you are referring to online: http://cecfoces.files.wordpress.com/2010/09/elmasri-navathe-fundamentals-of-database-systems-3rd-ed1.pdf
Could you please indicate where they say x-->a and y-->b DOES NOT IMPLY xy-->ab?
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