1. A key in a relational database table a. a proper subset of a candidate key. b
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Question
1. A key in a relational database table
a. a proper subset of a candidate key.
b. a proper superset of a candidate key.
c. a minimal superkey.
d. none of a., b., or c. are correct
2. If a relational database table is in Boyce-Codd normal form, it is also in
a. the first normal form.
b. the second normal form.
c. the third normal form.
d. all of a., b., and c.
3. _____________________ guarantee(s) that the number of index block accesses is equal to the level of the index structures.
a. Multilevel index
b. Dynamic hashing
c. B-tree/B+-tree
d. Multi-Way search tree
Explanation / Answer
1. A key in a relational database table
a. a proper subset of a candidate key.
b. a proper superset of a candidate key.
c. a minimal superkey.
d. none of a., b., or c. are correct
Answer is b. a proper superset of candidate key
A candidate key of a relation is a minimalsuperkey for that relation that is a set of attributes.
The relation does not have two distinct tuples with the same values of attributes.
There is no propersubset is a super key whith in the relation.
Employee (Employee ID, FullName, SSN, DeptID);
EmployeeID & SSN are Candidate keys in Employee table.
2. If a relational database table is in Boyce-Codd normal form, it is also in
a. the first normal form.
b. the second normal form.
c. the third normal form.
d. all of a., b., and c.
Answer is
Boyce-Codd normal form is one type of normalization.That is used to reduces redundancy and functional dependencies of data.
Even when a database is in 3rd Normal Form, still there would be anomalies resulted if it has more than one Candidate Key.
composite candidate keys with at least one attribute in common.
BCNF is based on the concept of a determinant.
A determinant is any attribute (simple or composite) on which some other attribute is fully functionally dependent.
A relation is in BCNF is, and only if, every determinant is a candidate key.
3. _____________________ guarantee(s) that the number of index block accesses is equal to the level of the index structures.
a. Multilevel index
b. Dynamic hashing
c. B-tree/B+-tree
d. Multi-Way search tree
Answer is c. B-tree/B+-tree
Each internal node in the B-Tree of order p is of the form <P1,, P2,, ... , Pq-1,< Kq-1,Prq-1>, Pq> where q <=p.
Each Pi is a tree pointer - a pointer to another node in the B-tree.
Each Pi is a data pointer - a pointer to a data block in the data file that contains a record with search key field value equal to Ki .
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