Chapter 5 Multiple Choice

When should you use a composite primary key?

-As identifiers of composite entities, in which each primary key combination is allowed only once in the M:N relationship -As identifiers of weak entities, in which the weak entity has a strong identifying relationship with the parent entity

Your boss needs you to show a specialization hierarchy that can reflect the relation between EMPLOYEES and its subtypes. What type of relationship do you need to show your boss?

1:1

Which of the answers below can be used to implement relationships among entities?

A foreign key or primary key

An entity cluster is considered "virtual"; or ___________; in the sense that it is not actually an entity in the final ERD.

Abstract

What is the benefit of the entity clustering?

Avoid the display of attributes to eliminate complications that result when the inheritance rules change.

In the enhanced-entity-relationship, what is the collection of entities in this set classified as?

Class

The _____ constraint specifies whether each entity supertype occurrence must also be member of at least one subtype

Completeness

The __ is used to develop an initial ERD that contains a few entities.

Data modeler

The result of a grouping operation on simple entities is called a(n) ______.

Entity cluster

Total completeness

Every supertype occurance must be a member of at least one subtype

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

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, always going to inherit all the attributes from a lower-level supertype

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

FASLE

What occurs when you have one entity in two 1:M relationships to other entities, which then produces an association among the other entities that is not expressed in the model?

Fan trap

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

Generalization

What is a specialization lattice

In which a subtype can have multiple parents

Which of the following is an example of a primary key?

Its constraint can be implicitly defined on the temporary tables.

Which of the following is an example of a foreign key?

Its value can be deleted from the child table.

Without the ______, the primary key inheritance rule changes.

Key attributes

In addition to the normal behavior, the EER model also supports specialization ______ where a subtype can have multiple parents

LATTICE

Which of the following is an entity cluster?

Location

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

How many entities can be represented in an entity cluster?

Multiple

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

Natural identifier

What is partial completeness?

Not every supertype occurrence is a member of a subtype

What is the best data type for a primary key?

Numeric

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

Only one

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

Primary

A single attribute and some combination of attributes can be a ______

Primary key

What is used by a data modeler when using a natural identifier of the entity being modeled and assuming that the entity has a natural identifier?

Primary key

________ relationships occur when there are multiple relationship paths between related entities

Redundant

What type of entitiy can have disjoint or overlappying entity subtypes

SUPERTYPE

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

Specialization

What do you add to the supertype table for a disjoint condition?

Subtype discriminator

Which of the following is a specialization hierarchy disjoint constraint scenario, in the 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.

What type of key can never be used as a search key?

Surrogate key

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

TRUE

What is the function of a primary key

The primary key is an attribute or a set of attributes that uniquely identify a specific instance of an entity.

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

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

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

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

a single abstract entity object

If we are creating subtypes for a car dealership. Why would an accountant be a subtype of an employee?

because it is identifiable with employees and has unique attributes

What would be considered part of the entity cluster for Location?

building, room

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

cluster

What type of keys are useful as identifiers of weak entities, where the weak entity has a strong identifier relationship with the parent entity?

composite key

The main concern with redundant relationships is that they remain _____ across the model.

consistent

Let assume that college football has many divisions. With this, each division has many players and each division has many teams. Given these "incomplete" business rules. What type of relationship is division in with the players and team?

division is in a 1:m relationship with team and players.

What type of line represents a total completeness constraint?

double horizontal line under the circle

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

false

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

false

56. Which of the answers below is not the most important characteristic of an entity?

foreign key

Which of the following can be null?

foreign key

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

natural

Which of the answers below is familiar to end users and forms part of their day-to-day business vocabulary?

natural key

The surrogate key has __ meaning in the uses environment.

no meaning

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

nonintelligent

What is the best way to manage unique values, since the database can use internal routines to implement a counter-style attribute that automatically increments values with the addition of each new row?

numeric

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

only once

What type of subtypes are subtypes that contain nonunique subsets of the supertype entity set?

overlapping

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

primary

When having a weak entity in a strong identifying relationship with a parent entity, what is used to represent the data model as two separate entities?

real-world object

49. 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

When looking at a college structure and their use of entity clusters, what are three things that would be considered part of the offerings?

semester, course, classes

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

should have the minimum number of attributes possible

What type of line represents a partial completeness constraint?

single horizontal line under the circle

What type of identifier relationship ensures that the dependent entity can exist only when it is related to the parent entity?

strong

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

surrogate

Using a data modeling point of view, what data refers to data whose values change over time and for which there must be kept a history of the data changes?

time variant

What is the general rule that is used when using entity clusters?

to avoid the display of attributes

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

When there is a discriminator of a weak entity how is the set specified?

using a dashed line