csc 335 exam 3 quizzes
weak
An entity set that does not have enough attributes to form a primary key on its own is called
B must be a subset of a
Assume that the functional dependency (FD) a -> B holds on a given schema R. Which of the following statements is not true -for every legal relation on R, whenever two tuples agree on a, they must also agree on B -a and B are subsets of R -B cannot be a subset of a -B must be a subset of a
R is in BCNF
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 -d = (AB, AC) is a decomposition of R that is in BCNF -R is in 3NF -R is in BCNF
d = {AD, BE, CDE} is a 3NF lossless-join and dependency-preserving decomposition of R
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
whenever we take the natural join of the tables on the smaller schema, we get precisely the same tuples as in r
Given R is a relation schema and r(R), a decomposition of R into smaller schemas is lossless iff _________________
For proper subset a of K, a -> R
Given that R is a relation schema and K is a candidate key for R. Which of the following statements is not true? -K functionally determines R -for proper subset a of K, a -> R -K must be a subset of R -all of the above -none of the above
all of the above
Given the schema R = (A, B, C) and 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
We can use the test in Alternative-1 to check whether or not A → B is preserved by this decomposition.
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? -d is a lossless-join 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-2 to check whether or not B → C is preserved by this decomposition. -The FD B → C is preserved by this decomposition.
A -> D
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 -> D AD -> EG A -> E A -> BCE
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
Car has total participation in owns while person has partial participation
Suppose that owns is a relationship set 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
a person can own at most one car, and a car can be owned by any number of people
Suppose that owns is a relationship set 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 and R
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
age
The attribute ______ is an example of a derived attribute
diamond
What geometric shape is used to show a relationship set in an E-R diagram?
multivalued attributes
When generating a relation schema from an entity set in an E-R diagram, we create separate schemas for ________________
If a -> B and a -> y, then a -> By
Which of the following FDs is not among Armstrong's Axioms: -If a -> B and a -> y, then a -> By -if a -> B, then ay -> By -if a -> B, and B -> y then a -> y -if B subset a, then a -> B
A simple attribute ID that sores a student id
Which of the following is an example of an atomic domain? -an attribute course_id where values encode both a course number and department number -a simple attribute iD that stores a student id -a multivalued attribute such as phone-number -a composite attribute such as address
address
the attribute _________ is an example of a complex attribute
true
true or false: A relation that is in BCNF is also in 3NF
true
true or false: functional dependencies are generalizations of the notion of keys
false
true or false: it is always possible to find a BCNF, lossless-join and dependency preserving decomposition for a given relation schema
relationship sets linking weak entity sets to their identifying strong entity sets
when reducing an E-R diagram to relation schemas, we do not generate schemas for ___________
partial key
A ____________ allows us to distinguish among all the entities of a weak entity set that depend on one strong entity
all of the above
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