+1 vote
180 views

Consider the relation $R(ABCDEG)$ and $FD's$ are

$\{AB \rightarrow C,AC \rightarrow B,AD \rightarrow E,B \rightarrow D,BC \rightarrow A,E \rightarrow G\}$

then the decomposition$\{ABC,ACDE,ADG\}$

1. is lossless and not dependency preserving
2. is not lossless and dependency preserving
3. is lossless and dependency preserving
4. is not lossless and not dependency preserving
edited | 180 views

lossless and not dependency preserving.

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Their is no attribute F given in relation R
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yes i read wrong .now i am updating
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Nice explanation.
+1 vote

It is lossless but not dependency preserving lossless is easy

for dependency preserving

B->D& E->G are not there in relation

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can you please explain why it is lossless
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How you know about lossless: when Two relation R1 and R2 are made from original relation then common elements from these two relations must be a candidate key of any relation.

Now look here:

ABC and ACDE here common element AC is Candidate key of R1. Now relation will be ABCDE.

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Hint:AD->G is hidden relation bcz AD->E  E->G so we can say AD->G   merge ABC ACDE  common part AC is superkey

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Yes Your correct and its lossless @anu007 and @akshat sharma
+1 vote

Option (A) :It is lossless but not dependency preserving lossless.

Explaination :-

Dependency preserving: Even if there are many functional dependencies in Relation R, all of them won't be applicable, Only functional dependencies which contain only these attributes:-

{ABC} AB->C , AC->B , BC-> A

The lost functional dependencies are B->D and E->G, They cannot be derived even when the table is  joined.

lossless:-

There are two types lossy decomposition(when extra tuples are added when the tables are re-joined) and lossless decomposition(no extra tuples gets added, Original tuples are reformed)

The condition for lossless join is : If the common attribute is the key in one of the tables.

Between table {ABC and ACDE} AC is key of table {ABC} and hence between table {ACDE} and {ADC}, AD is common and key attribute of table {ADG and ACDE}

Hence, the table is lossless.

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it is lossless
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Yes its, lossless.

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+1 vote