Chapter 6 Databases HW
Desire to reduce replication
All of the following are reasons for leaving a schema in a lower normal form except
lossless decomposition
For a relational decomposition, the property of being able to get back exactly the original relation by joins is
for each X value there is only one Y value
If X and Y are sets of attributes of relation R, we say that Y is functionally dependent on X if
transitive
If a relation is 2NF but not 3NF, it must have which type of functional dependency?
X is not a superkey
If a relation is 3NF but not BCNF, it must have a non-trivial functional dependency X → A such that
has more rows than the original table
If a relational decomposition is not lossless, doing joins to recreate the original table may produce a table that
{A,B,D} must also be a candidate key for R {A,B} or {A,C} or {B,C} must also be a candidate key for R {A,B,C,D} must also be a candidate key for R Answer: none of these
If set S{A,B,C} is a candidate key for the relation R(A,B,C,D,E), then which of the following must be true
{A,B,C,D} is also a superkey for R
If set S{A,B,C} is a superkey for the relation R(A,B,C,D,E), then
B → C
In a relation R(A, B, C, D), which of the following would prove that R is not 3NF?
every attribute of the universal relation appears in at least one relation
In relational decomposition of a universal relation, the property of attribute preservation requires that
all the attributes on both sides of each dependency appear in the same relation
In relational decomposition of a universal relation, the property of dependency preservation requires that
A → C
In the relation R(A, B, C, D), having the composite key {A,B}, which of the following FDs would demonstrate that the relation is not 2NF?
C → D
In the relation R(A, B, C, D), having the composite key {A,B}, which of the following FDs would demonstrate that the relation is not 3NF?
Decompose R into R1(A,B,C,D) and R2(D)
In the relation R(A,B,C,D) if D is multivalued and the apparent key is A, which of the following is NOT an acceptable way to create a first normal form table for this schema?
the join produces the same tuples as the original relation
In the relational model, a projection is lossless if
is created by a lossy join
In the relational model, a spurious tuple is one that
simple
In the relational model, all of the following are types of dependencies that have been shown to lead to update anomalies EXCEPT
a candidate key a superkey a composite key Answer: none of these
In the relational model, every determinant is always
if two rows have the same A value, they must have the same B value
In the relational model, if A functional determines B, it means that
is lossless, but may not preserve dependencies
It is always possible to find a Boyce-Codd Normal Form decomposition that
3NF
It is always possible to find a dependency preserving lossless decomposition for _______.
3rd
The essence of _______ normal form is that each non-key attribute is functionally dependent on the entire key, and on no other attribute.
3NF
The highest normal form that always allows us to preserve functional dependencies is
synthesis
The normalization process in which we find and group together functional dependencies with the same determinant is called
analysis
The normalization process that starts with a universal relation and uses decomposition to produce a set of normalized relations is called
identifying and removing each violation of BCNF from a universal relation
The standard decomposition algorithm for BCNF requires
The standard mapping of an E-R diagram to a relational model results in a schema that is close to normalized
Using an E-R diagram can be helpful in designing a normalized schema because
a superkey of one of the relations
We can ensure that a binary decomposition is lossless if the set of common attributes in the two relations is
improving efficiency
Which of the following is not one of the major objectives of normalization?
Normalization
_______ means putting a relation into a higher normal form.
composite key
A _______ key is a key that consists of more than one attribute.
candidate
A _______ key is a superkey such that no proper subset of its attributes is itself a superkey.
trivial
A functional dependency in which the attributes on the right hand side are included in the determinant is called
no nonkey attribute is dependent on another nonkey attribute
A relation having only one candidate key is third normal form if it is 2NF and
every determinant is a superkey
A relation is Boyce-Codd Normal Form if
every attribute is single-valued for each tuple the domains of the attributes are atomic each cell of the table can contain only one value Answer: all of these
A relation is first normal form if
first
A relation is in _______ normal form if, and only if, every attribute is single-valued for each tuple.
every nonkey attribute is dependent on the entire key
A relation is second normal form if it is 1NF and