Talk:Multivalued dependency

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"tuple-generating" needs definition or Wikilinking. --Dweller 12:06, 11 August 2006 (UTC)[reply]

Done. I'm considering changing the Greek letters to X, Y, Z's for readability, but I'm not sure how everybody thinks about that.--Citral 15:53, 11 August 2006 (UTC)[reply]

I concure. It's kinda confusing as it is --markild 15:21, 22 March 2007 (UTC)[reply]

In "Formal definition", isn't t4 unnecessary, due to symmetry? t1 and t2 are interchangeable, and it doesn't say t3 and t4 have to be distinct and there's no statement relating t3 and t4. If t4 were left out, it would make the definition easier to follow, I think. -- 65.94.54.139 03:44, 25 February 2007 (UTC)[reply]

Ok, I guess I see why it was stated that way now. Intuitively, "the other two possible combinations must also exist". - 65.94.54.139 04:02, 25 February 2007 (UTC)[reply]

Under "interesting properties": those properties are interesting... but why are they true? They dont seem to make any sense to me. -- anon

I guess I could post a proof on the article page, but wouldn't that obfuscate the article and be against the WP policies? --Citral 21:05, 24 June 2007 (UTC)[reply]

Context[edit]

Would be useful to add some context as to how MVDs rise. For example, could an MVD rise from the physical implementation of a robust ERD?

What kind of design omissions create the conditions for the presence of MVDs? Can MVDs be eliminated by improving the design process and by avoiding use of flawed design languages? —Preceding unsigned comment added by Lgreco (talk • contribs) 18:25, 27 May 2008 (UTC)[reply]

I changed the ordering of the first four tuples in the example, so that it exactly mirrors the formal definition to improve the consistency of the article.

83.78.128.28 (talk) 19:40, 1 June 2008 (UTC)[reply]

Example expansion[edit]

So the example states: there are two multivalued dependencies in this relation: {course} $\twoheadrightarrow$ {book} and equivalently {course} $\twoheadrightarrow$ {lecturer}.

Does that also imply:

{course} $\twoheadrightarrow$ {book, lecturer}?

If so how would you state that last relation in words? --Fxer (talk) 04:11, 13 October 2011 (UTC)[reply]

That MVD is trivial, because it involves all atributes of the relation. Miparnisari (talk) 18:43, 1 February 2015 (UTC)[reply]

Clarification[edit]

if we denote by (x,y,z) the tuple having values for α, β, R−α−β collectively equal to x, y, z, correspondingly, then whenever the tuples (a,b,c) and (a,d,e) exist in r, the tuples (a,b,e) and (a,d,c) should also exist in r. What Does should exist mean? Is it expected to exist or permitted to exist ? -Emakalam (talk) 20:57, 23 February 2015 (UTC)[reply]

Repeatition of data when there's an MV[edit]

What exacly is the reason when adding a new value to a field b when a ->> b, and another md a ->> c exists, and the values contained in the table for c can be described as set C, it's needed to add to the table b cross C, when I want to add a new value b? I currently learn a course in databases and couldn't understand the reason behind it. It also not explained in the textbook, or here. It just seems obvious. Galzigler (talk) 16:01, 2 February 2018 (UTC)[reply]

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