quiz 2

_____ is the bottom-up process of identifying a higher-level, more generic entity supertype from lower-level entity subtypes.

Generalization

Which of the following is a specialization hierarchy disjoint constraint scenario in case of partial completeness?

Subtype discriminator can be null.

A partial completeness constraint is represented by _____

a single horizontal line under a circle

A total completeness constraint is represented by a _____.

double horizontal line under a circle

The extended entity relationship model (EERM) is sometimes referred to as the _____.

enhanced entity relationship model

Disjoint subtypes are subtypes that contain nonunique subsets of the supertype entity set.

false

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.

false

Overlapping subtypes are subtypes that contain a unique subset of the supertype entity set.

false

The property of a subtype discriminator enables an entity supertype to inherit the attributes and relationships of the subtype.

false

To model time-variant data, one must create a new entity in an M:N relationship with the original entity

false

Within a specialization hierarchy, a supertype can exist only within the context of a subtype.

false

The property of _____ enables an entity subtype to inherit the attributes and relationships of the supertype.

inheritance

A _____ key is a real-world, generally accepted identifier used to uniquely identify real-world objects.

natural

In the context of total completeness, in a(n) _____, every supertype occurrence is a member of at least one subtype.

overlapping constraint

The most important characteristic of an entity is its _____ key, used to uniquely identify each entity instance

primary

According to the "preferably single-attribute" characteristic of a primary key, the primary key:

should have the minimum number of attributes possible.

A(n) _____ is the attribute in the supertype entity that determines to which entity subtype each supertype occurrence is related.

subtype discriminator

A design trap occurs when a relationship is improperly or incompletely identified and is therefore represented in a way that is not consistent with the real world.

true

An entity supertype can have disjoint or overlapping entity subtypes.

true

Entity supertypes and subtypes are organized in a specialization hierarchy.

true

One important inheritance characteristic is that all entity subtypes inherit their primary key attribute from their supertype.

true

The completeness constraint can be partial or total.

true

The entity supertype contains common characteristics, and the entity subtypes each contain their own unique characteristics.

true

The relationships depicted within the specialization hierarchy are sometimes described in terms of "is-a" relationships.

true

Nonoverlapping subtypes are subtypes that contain a(n) _____ subset of the supertype entity set.

unique