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The correct option is (b) False

The EXPLANATION: IF a SYSTEM supports a native VALID time type, then the system can detect and prevent OVERLAPPING time intervals.

Correct option is (C) Snapshot

Easiest EXPLANATION: The value of the DATA at a particular time is called as a snapshot. This is USED in temporal data.

Right CHOICE is (a) True

For EXPLANATION: Crosstabs may be USEFUL for the users but they are not desirable in a database system because the queries would get more COMPLICATED DUE to the addition of cross tabs.

The correct choice is (b) Denormalization

Easiest explanation: The process of making a normalized SCHEMA unnormalized is CALLED as denormalization. Designers use it to TUNE performance of SYSTEMS to support time-critical operations.

Right option is (a) The attribute name has a unique meaning in the database

The EXPLANATION: Unique role assumption MEANS that the attribute names must have unique meaning in the database. This prevents us from using the same attribute to MEAN different things in different SCHEMAS.

The correct option is (d) None of the mentioned

The EXPLANATION: All of the mentioned normal FORMS i.e. BCNF, PJNF, 5NF exist. BCNF is Boyce Codd normal form, 5NF is the FIFTH normal form and PJNF is project JOIN normal form.

Correct CHOICE is (d) 4

The BEST I can explain: If a relational schema is in 4NF and A is a subset of R and B is also a subset of R then it is that A is a SUPERKEY is a trivial MULTI values dependency.

Correct option is (b) Closure

To EXPLAIN: The closure is a set of all FUNCTIONAL and MULTI values dependencies implied by a set of functional dependencies on a given RELATION. It is denoted by giving a “+” superscript.

Correct OPTION is (a) EQUALITY generating DEPENDENCIES

For explanation I would say: Functional dependencies are sometimes referred to as equality generating dependencies because they REQUIRE other tuples of a CERTAIN form to be present in the relation.

Correct choice is (b) TUPLE GENERATING dependencies

For EXPLANATION I would say: Multi valued dependencies are also called as tuple generating dependencies because they require other tuples of a certain form to be PRESENT in the RELATION.

Right answer is (B) False

For explanation I would say: SQL does not SPECIFY a WAY to mention functional DEPENDENCIES. Functional dependencies are just used for theoretical improvement of database while implementing them in SQL later.

Correct choice is (a) States a method to DECOMPOSE a RELATION SATISFYING BCNF

For explanation I would say: If a relation is not in BCNF, it can be DECOMPOSED into simpler relations that are in BCNF. The BCNF decomposition ALGORITHM states a method to decompose a relation satisfying BCNF.

The correct choice is (a) CANONICAL cover

Explanation: A Canonical cover Fc for F is a set of dependencies such that F LOGICALLY IMPLIES all dependencies in Fc, and Fc logically implies all dependencies in F. In Fc, no functional DEPENDENCY should contain an extraneous attribute and each left side of functional dependency should be unique.

The correct option is (d) Functionally DETERMINED

To explain: If B is an ATTRIBUTE and A→B, Then B is SAID to be functionally determined by a.

Correct option is (d) All of the mentioned

Best EXPLANATION: Applying the union rule to the given question, we get, A→BC is TRUE. The other two OPTIONS are specified in the question itself.

The CORRECT choice is (a) True

For explanation I would say: All functional dependencies are transitive. This is the TRANSITIVITY rule of Armstrong’s AXIOMS.

Correct option is (d) They cannot generate incorrect FUNCTIONAL dependencies

Explanation: ARMSTRONG’s AXIOMS are CALLED as sound axioms because they do not generate incorrect functional dependencies.

Right CHOICE is (c) F+

The best EXPLANATION: If F is a set of FUNCTIONAL DEPENDENCIES, then the closure of F is denoted by F+. It is the set of all functional dependencies logically implied by F.

Right choice is (b) False

Easy explanation: The fourth NORMAL form EXISTS and is DIFFERENT from the Boyce Codd normal form which is CALLED as BCNF.

The CORRECT ANSWER is (d) Each attribute in X-Y is a candidate key for R

To elaborate: Each attribute in X-Y is a candidate key for R is not a NECESSARY CONDITION for the third normal form in the case of X →Y. X→Y is trivial and X is the superkey of R are necessary conditions for the third normal form.

Right choice is (d) All of the mentioned

For explanation: Primary keys, Functional dependencies, CHECK CLAUSE are all USED to EXPRESS database consistency.

Right option is (c) Y is the superkey for the RELATIONAL schema R

Easiest explanation: Y does not need to be a superkey of the relation for the given functional dependency to SATISFY BCNF. X→ Y must be trivial and X must be the superkey of the relation R.

The correct choice is (a) X ⊂ Y

For explanation: X→ Y is SAID to be TRIVIAL if X is a SUBSET of Y. THUS X ⊂ Y implies X→Y is trivial.

The correct ANSWER is (C) Each and every legal instance satisfies the functional dependency

Explanation: X →Y HOLDS on a schema k(K) if each and every legal instance satisfies the functional dependency. Even if one instance does not SATISFY the functional dependency X→ Y does not hold on a schema.

The correct CHOICE is (c) Super key

For explanation I would say: If K →R then k is said to be the superkey of R i.e. K uniquely identifies EVERY tuple in the relation R.

The correct ANSWER is (b) False

To explain: Redundancy is never desired in a RELATIONAL schema, it MAKES data retrieval very difficult.

Correct answer is (a) 1

To explain I would say: If all the domains are atomic then the relational schema is in FIRST (1) normal FORM. That is, the domains must be INDIVISIBLE.

Correct choice is (a) LOSSLESS decomposition

Best EXPLANATION: If the decomposition is able to represent all the facts about the relation then such a decomposition is CALLED as a lossless decomposition. Lossless DECOMPOSITIONS are generally preferred.

Right choice is (c) FUNCTIONAL dependencies

For explanation I would say: The dependency RULES SPECIFIED by the DATABASE designer are known as functional dependencies. The normal forms are BASED on functional dependencies.