First, come up with a relation with some functional dependencies. At least one of the functional dependencies violates BCNF and at least one other of the functional dependencies makes it not dependency-preserving. Now, do lossless-join decomposition into BCNF although it may not be dependency-preserving.
Second, come up with a relation with some functional dependencies that make it dependency-preserving but not lossless-join.
Explain every step.
some basic definitions:-
dependency preservation decomposition:-F
Relational schemas R with FD set F decomposed into relations R1,R2,R3,...,Rn with FD sets F1,F2,F3,...,Fn then
if [F1UF2UF3U...UFn] is equal to F then it is dependency preservation decomposition.
Lossless join decomposition:-
Relational schemas R with FD set F decomposed into relations R1,R2,R3,...,Rn subrelations
if R1 join R2 join R3....join Rn is equal to R then it is lossless join decomposition.
A very simple trick to check if lossless join had occured or not is check if two relations which are being joined have atleast one attribute in common and atleast in one relation that common attribute is key.
Now, a relation which is not in BCNF and when decomposed to form BCNF it can't be dependency preserved:-
First, come up with a relation with some functional dependencies. At least one of the functional...
Which of the following statements is CORRECT? (1 Point) Select one: O Every relation that is in 3NF have no redundancy. A relation that is in BCNF could have some redundancy. Every relation that is in 3NF is also in BCNF. For Every relation that is not in BCNF, we can always find a lossless-join and dependency-preserving decomposition of the relation into BCNF relations. All of the above. O None of the above
Which of the following statements is CORRECT? (1 Point) Select one: Every relation that is in 3NF have no redundancy. O A relation that is in BCNF could have some redundancy. Every relation that is in 3NF is also in BCNF. For Every relation that is not in BCNF, we can always find a lossless-join and dependency-preserving decomposition of the relation into BCNE relations All of the above. None of the above.
Which of the following statements is CORRECT? (1 Point) Select one: O Every relation that is in 3NF have no redundancy. O A relation that is in BCNF could have some redundancy. o Every relation that is in 3NF is also in BCNF. For Every relation that is not in BCNF, we can always find a lossless-join and dependency-preserving decomposition of the relation into BCNF relations All of the above. None of the above
Dependency Very Good dependency (key dependency) : XA where Table Very good If all dependencies in a table are '"very good", the table is in BCNF X is a candidate key Good Good dependency: X-> A where If all dependencies in a table are "very good" or "good", the table is in 3NF X is not a candidate key X is a part of a candidate key A is prime attribute Bad Bad dependency (Transitive Dependency): X A where If...
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