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Consider a database R = {Ra} with Ra = {A1, A2, A3, A4, A5, A6} and the dependencies F = {A1 → A2, A2 → A3, A3 → A4, A4 → A2, A3 → A5}.

Consider R1 = {A1, A2}, R2 = {A2, A3, A4}, R3 = {A1, A2, A5}, R4 = {A3, A4}.

How can I tell if R1,R2,R3,R4 is a losseless-join decomposition

philipxy
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Or Ami
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  • What database technology, query language etc. do you use? –  Dec 14 '14 at 17:41
  • Its a theoretical question, we haven't learned any specific language – Or Ami Dec 14 '14 at 18:00
  • The question is not clear though. –  Dec 14 '14 at 18:01
  • I think the question is clear, but the research effort is not. – Lucia Pasarin Dec 14 '14 at 23:14
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    @ciuak, if you don't know what you're talking about, then don't comment. Since the question is about functional dependency theory, it should be clear to anyone knowledgeable (not you, apparently) that the "database technology" is "relational technology" and "which query language" is completely besides the point, since functional dependency theory is independent of query language. – Erwin Smout Dec 14 '14 at 23:20

1 Answers1

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The decomposition you gave cannot possibly be lossless in any meaning of the word because your input schema has A6 but your decomposition does not mention it.

Erwin Smout
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