Database Applications chapter 5

At the implementation level, the supertype and its subtype(s) depicted in a specialization hierarchy maintain a(n) _____ relationship.

1

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

FALSE

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

Generalization

Composite primary keys are particularly useful as identifiers of composite entities, where each primary key combination is allowed only once in the _____ relationship.

M:N

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

Subtype discriminator can be null.

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

Supertype has optional subtypes.

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

An entity cluster is formed by combining multiple interrelated entities into _____.

a single abstract entity object

A partial completeness constraint is represented by _____.

a single horizontal line under a circle

The purpose of an entity _____ is to simplify an entity-relationship diagram (ERD) and thus enhance its readability.

cluster

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

A(n)_____ is a generic entity type that is related to one or more entity subtypes.

entity supertype

The default comparison condition for the subtype discriminator attribute is the _____ comparison.

equality

An entity cluster is a "virtual" entity type used to represent multiple entities and relationships in the ERD.

false

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

false

Specialization is the top-down process of identifying lower-level, more specific entity subtypes from a higher-level entity supertype.

false

The function of the primary key is to describe an entity.

false

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

false

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

inheritance

A specialization hierarchy can have _____ level(s) of supertype/subtype relationships.

many

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

natural

If one exists, a data modeler uses a _____ as the primary key of the entity being modeled.

natural identifier

The "_____" characteristic of a primary key states that the primary key should not have embedded semantic meaning.

nonintelligent

Overlapping subtypes are subtypes that contain _____ subsets of the supertype entity set.

nonunique

Within a specialization hierarchy, every subtype can have _____ supertype(s) to which it is directly related.

only one

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

overlapping constraint

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

overlapping constraint

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

primary

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

primary

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.

security-compliant

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

should have the minimum number of attributes possible.

The _____ depicts the arrangement of higher-level entity supertypes (parent entities) and lower-level entity subtypes (child entities).

specialization hierarchy

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

subtype discriminator

A _____ is a primary key created by a database designer to simplify the identification of entity instances.

surrogate key

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

A subtype contains attributes that are common to all of its supertypes.

true

An entity supertype can have disjoint or overlapping entity subtypes.

true

At the implementation level, the supertype and its subtype(s) depicted in the specialization hierarchy maintain a 1:1 relationship.

true

Entity subtypes do not inherit the relationships in which the supertype entity participates.

true

Implementing overlapping subtypes requires the use of one discriminator attribute for each subtype.

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.

true

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

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

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

true

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

unique

The "_____" characteristic of a primary key states that the primary key must uniquely identify each entity instance, must be able to guarantee unique values, and must not contain nulls.

unique values