Database Systems Exam 3

A relation that is in 3NF but not in BCNF can suffer from the following problems _________________ Redundancy The need to use null values All of the above None of the above

All of the above

Given the schema R = (A, B, C) and a set a set F = { A → BC, B → C, A → B, AB →C} of FDs that holds on R. Which of the following statements is correct? We can show that the attribute B is extraneous in the FD A → BC We can show that the attribute C is extraneous in the FD A → BC We can show that the attribute B is extraneous in the FD AB → C All of the above None of the above

All of the above

Suppose that a relation schema R is decomposed into the set of relation schemas {R1, R2, ..., Rn}. Then, which of the following statement(s) is true: Each Ri must be a subset of R for i = 1, 2, ..., n. The decompsoition is lossless-join iff for every legal relation r(R), the natrural join of the projection of r on the smaller schemas is equl to r. If the decomposition is dependency preserving, then when the DB is updated, the DBMS needs to only ensure that the updated tables do not violate FDs. Otherwise, the DBMS needs to perform a natural join to check for that. All of the above None of the above

All of the above

It is always possible to find a BCNF, lossless-join and dependency preserving decomposition for a given relation schema.

False

Given that R is a relation schema and K is a candidate key for R. What cannot be True?

For proper subset α of K, α → R.

Given R = (A, B, C) is a schema and F = { BC → A, A → B} is a set of FDs that hold on R. Which of the following statements is not true? BC is a candidate key for R. R is in 3NF d = (AB, AC) is a decomposition of R that is in BCNF. R is in BCNF

R is in BCNF

A relation that is in BCNF is also in 3NF.

True

Functional dependencies are generalizations of the notion of keys.

True

Let R = (A, B, C) be a schema and F = {A → B, B → C) be a set of FDs that hold on R. Also assume that d=(AC, BC) is a decomposition of R. Which of the following statements is not true? A → C is a member of F+. We can use the test in Alternative-2 to check whether or not B → C is preserved by this decomposition. The FD B → C is preserved by this decomposition. We can use the test in Alternative-1 to check whether or not A → B is preserved by this decomposition.

We can use the test in Alternative-1 to check whether or not A → B is preserved by this decomposition.

Suppose that owns is a relationship set between between entity sets person and car. If the mapping cardinality of owns is many to one from person to car, then this would mean ____________

a person can own at most one car, and a car can be owned by any number of people.

Let R = (A, B, C, D, E, G) be a schema and F = { A → BC, B → E, CD → EG} be a set of FDs that holds on F. Which of the following FDs is not a member of F+? A → E A → D A → BCE AD → EG

a → d

The attribute _______ is an example of a complex attribute.

address

The attribute _______ is an example of a derived attribute.

age

Given R = (A, B, C, D, E) is a schema and F = {A → D, B → E, DE → C } is a set of FDs that hold on R. Which of the following statements is not true? d = {AD, BE, ABC} is a lossless-join BCNF decomposition of R d = {DEC, AD, AB, BE} is a lossless-join and dependency preserving BCNF decomposition of R Every candidate key of R must contain the attributes A and B AB is the only candidate key for R d = {AD, BE, CDE} is a 3NF lossless-join and dependency-preserving decomposition of R

d = {AD, BE, CDE} is a 3NF lossless-join and dependency-preserving decomposition of R

What geometric shape is used to show a relationship set in an E-R diagram?

diamond

Armstrong's Axioms:

if α → β, then αγ → βγ If α → β, and β → γ then α → γ If β ⊆ α, then α → β

When generating a relation schema from an entity set in an E-R diagram, we create separate schemas for ____________________

multivalued attributes

A _____________________ allows us to distinguish among all the entities of a weak entity set that depend on one strong entity.

partial key

When reducing an E-R diagram to relation schemas, we do not generate schemas for ______________

relationship sets linking weak entity sets to their identifying strong entity sets

An entity set that does not have enough attributes to form a primary key on its own is called ________

weak

Given R is a relation schema and r(R). A decomposition of R into smaller schemas is lossless iff _______________________

whenever we take the natural join of the tables on the smaller schemas, we get precisely the same tuples as in r

Assume that the functional depnedency (FD) α → β holds on a given schema R. What cannot be True?

β must be a subset of α

Suppose that you are given an E-R diagram that consists of a m:1 relationship set R from an entity set A to an entity set B. Also suppose that the participation of A in R is total. Then, in the reduction of this E-R diagram into relation schemas, the schemas you get from __________________ should be combined together.

A and R

Which of the following is an example of an atomic domain?

A simple attribute ID that stores a student id

Suppose that owns is a relationship set between between entity sets person and car. If every car must participate in the relationship set owns while not every person must participate in owns, then this would mean ____________

Car has total participation in owns while person has partial participation.