Chapter 5 Flashcards
According to the “preferably single-attribute” characteristic of a primary key, the primary key:
a) must be composed of attributes that are free from security risks or violations.
b) must be able to guarantee unique attribute values.
c) should have the minimum number of attributes possible.
d) should have embedded semantic meaning associated with each attribute.
c) should have the minimum number of attributes possible.
The function of the primary key is to describe an entity.
a) true
b) false
a) true
Implementing nonoverlapping subtypes requires the use of one discriminator attribute for each subtype.
a) true
b) false
b) false
Some designs use redundant relationships as a way to simplify the design.
a) true
b) false
a) true
Within a specialization hierarchy, every subtype can have _____ supertype(s) to which it is directly related.
a) zero
b) only one
c) many
d) one or many
b) only one
One important inheritance characteristic is that all entity subtypes inherit their _____ key attribute from their supertype.
a) primary
b) natural
c) surrogate
d) foreign
a) primary
Entity supertypes and subtypes are organized in a specialization hierarchy.
a) true
b) false
a) true
Overlapping subtypes are subtypes that contain _____ subsets of the supertype entity set.
a) exclusive
b) null
c) solitary
d) nonunique
d) nonunique
The relationships depicted within the specialization hierarchy are sometimes described in terms of “is-a” relationships.
a) true
b) false
a) true
In specialization hierarchies with multiple levels of supertype and subtypes, a lower-level subtype can inherit only a few of the attributes and relationships from its upper-level supertypes.
a) true
b) false
b) false
A specialization hierarchy can have _____ level(s) of supertype/subtype relationships.
a) many
b) zero
c) only one
d) one or many
a) many
_____ is the bottom-up process of identifying a higher-level, more generic entity supertype from lower-level entity subtypes.
a) Generalization
b) Total completeness
c) Normalization
d) Specialization
a) Generalization
The completeness constraint can be partial or total.
a) true
b) false
a) true
The “_____” characteristic of a primary key states that the selected primary key must not be composed of any attribute(s) that might be considered a violation.
a) nonintelligent
b) unique values
c) preferably single-attribute
d) security-compliant
b) unique values
A _____ key is a real-world, generally accepted identifier used to uniquely identify real-world objects.
a) foreign
b) surrogate
c) natural
d) primary
c) natural
Specialization is the top-down process of identifying lower-level, more specific entity subtypes from a higher-level entity supertype.
a) true
b) false
a) true
At the implementation level, the supertype and its subtype(s) depicted in the specialization hierarchy maintain a 1:1 relationship.
a) true
b) false
a) true
The default comparison condition for the subtype discriminator attribute is the _____ comparison.
a) less than
b) equality
c) greater than
d) nonequality
b) equality
Which of the following is a specialization hierarchy overlapping constraint scenario in case of partial completeness?
a) Supertype has optional subtypes.
b) Subtype discriminators cannot be null.
c) Subtype sets are unique.
d) Subtype does not have a supertype.
a) Supertype has optional subtypes.
When selecting a foreign key placement for a 1:1 relationship, place the PK of the entity on the mandatory side in the entity on the optional side as a FK, and make the FK mandatory when _____.
a) both sides are mandatory
b) both sides are optional
c) one side participates in another relationship
d) one side is mandatory and the other side is optional
d) one side is mandatory and the other side is optional
