Chapter 3

What is true of an overlap figure regarding a rental unit? A rental unit must be either an apartment or a house, and cannot be both at the same time. A rental unit can be an apartment, house or just a rental unit; it may not be more than one at the same time. A rental unit must be either an apartment or a house, and could be both. A rental unit can be an apartment, a house or just a rental unit. It could be both an apartment and a house at the same time.

A rental unit can be an apartment, a house or just a rental unit. It could be both an apartment and a house at the same time.

Given the following entities, which of the choices below would be the most complicated? Automobile: VIN, EngineSize, NumberOfDoors, NumberOfPassengers, FuelType, TransmissionSUV: VIN, EngineSize, NumberOfPassengers, NoWheelDrive, FuelType, TransmissionTruck: VIN, EngineSize, NoWheelDrive, FuelType, Transmission, Payload Answers: Define one vehicle entity type to hold all entities. Define a separate entity type for each entity. Define a supertype called vehicle and make each of the entities subtypes. Keep only the Truck entity type.

Define one vehicle entity type to hold all entities.

A subtype is a generic entity that has a relationship with one or more entities at a lower level

False

Packaged data models use an entity type to store union data

False

The total specialization rule states that an entity instance of a supertype is allowed not to belong to any subtype

False

Which of the following is true of packaged data models? Relationships are connected to the highest-level entity type in an order that makes sense. All subtype/supertype relationships follow the total specialization and disjoint rules. No entities on the many sides of a relationship can be weak. All weak entities are considered strong.

Relationships are connected to the highest-level entity type in an order that makes sense.

Contrast the overlap rule to the disjoint rule

The disjoint subtype is used when there are two separate entities that do not overlap. The overlap subtype rule specifies that an entity can be more than one subtype. For example, a store employee at Target could also be a customer at that store

In packaged data models, all subtype/supertype relationships follow the ________ and ________ rules. partial specialization; disjoint total specialization; disjoint total specialization; overlap partial specialization; overlap

Total specialization; overlap

An entity cluster can have a relationship with another entity cluster much the same way that an entity can have a relationship with another entity.

True

It is easier to share information across organizations if companies in the same industry use the same universal data model as the basis for their organizational databases.

True

Specialization is the reverse of generalization

True

Supertype/subtype relationships should not be used when the instances of a subtype participate in no relationships which are unique to that subtype.

True

The most important challenge of customizing a purchased data model is determining the business rules that will be established through the data model.

True

How is the data modeling process different when starting with a purchased solution?

When an organization starts with a purchased solution, there is less time and skill to set up. The company is able to focus on the details of the entities instead.

The process of defining a more general entity type from a set of more specialized entity types is called: generalization specialization normalization extrapolation

generalization

All of the following are advantages of packaged data models EXCEPT packaged data models can be built using proven components evolved from cumulative experiences. projects take less time and cost less. the data model is easier to evolve. more one-to-one relationships give the data model more flexibility.

more one-to-one relationships give the data model more flexibility.

An attribute of the supertype that determines the target subtype(s) is called the determinant subtype decision disjoint indicator subtype discriminator

subtype discriminator

In a supertype/subtype hierarchy, subtypes that are lower in the hierarchy inherit attributes from not only their immediate supertype but from all ________ in the hierarchy. subtypes supertypes constraints dimensions

supertypes

It is easy to miss the opportunity to visualize future requirements shown in the full data model when using a packaged data model.

true