# Proving Join Dependencies in MVD

I have a question regarding natural join operations in multivalued dependencies. I know that a join operator joins two tables on similair attributes, however I have a hard time to figure out how to approach the following excersise. A nudge in the right directon will be helpful±

There are 7 tuples, B (meeting nr), T (time of meeting B), L (location of meeting b), I (organizer of B), D (participant of B), R (rol of participant D in B), E (email of D).

Several meetings can be held at the same time but at another location, an organizer is also an participant, each participant has on role at most, a participant can have multiple email addresses.

I need to prove or disprove the following statement:

BTLIDRE = BE \natural BTLIDR
BTLIDRE = BDRE \natural BTLI
BTLIDRE = BD \natural BTLIDR


My initial reasoning was that since both sides contain common attributes either B or BD, all those statemments are valid, however that didn't seems to be correct according to the answers. How can I approach this question?

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What's the source of your conviction that we will all know what you mean by \natural? –  joriki Jan 24 '13 at 12:32
the natural join operator also seen in sql syntax –  Setsuna Jan 24 '13 at 12:44
What are these seven tuples tuples of? In what sense does the juxtaposition of two or more names of such tuples represent a table? It seems weird that things like meeting numbers should be tuples; I would have expected them to be attributes in a table, i.e. entries in tuples. Perhaps you meant "There are $7$-tuples", with a hyphen, and the letters label the seven entries of these $7$-tuples? If so, it still remains to clarify what the juxtaposition of these labels denotes. –  joriki Jan 24 '13 at 12:54
Yes, I meant there are 7 tuples –  Setsuna Jan 24 '13 at 12:58
I don't understand. "Yes" in the sence of reconfirming what you had originally written? Or "Yes" in the sense of agreeing with my considerations? In the latter case, you forgot the hyphen yet again. –  joriki Jan 24 '13 at 13:00