Modern Database Management - Chapter 3
All of the following are advantages of packaged data models EXCEPT:
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:
none of the above.
In a supertype/subtype hierarchy, each subtype has:
only one supertype.
The ________ rule states that an entity instance can simultaneously be a member of two (or more) subtypes.
overlap
The subtype discriminator is a composite attribute when there is a(n):
overlap rule.
The ________ rule specifies that an entity instance of a supertype is allowed not to belong to any subtype.
partial specialization
Packaged data models:
require customization.
The process of defining one or more subtypes of a supertype and forming relationships is called:
specialization.
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.
supertypes
Subtypes should be used when:
there are attributes that apply to some but not all instances of an entity type.
The ________ rule specifies that each entity instance of the supertype must be a member of some subtype in the relationship.
total specialization
In packaged data models, all subtype/supertype relationships follow the ________ and ________ rules.
total specialization and overlap
A generic or template data model that can be reused as a starting point for a data modeling project is called a(n):
universal data model.
All of the following are steps to using a packaged data model EXCEPT:
utilize all business rules that come with the packaged data model.
In packaged data models, strong entities always have ________ between them.
M:N relationships
Which of the following is a generic entity type that has a relationship with one or more subtypes?
Supertype
An entity instance of a subtype represents the same entity instance of the supertype.
TRUE
One of the major challenges in data modeling is to recognize and clearly represent entities that are almost the same.
TRUE
Which of the following is a completeness constraint?
Total specialization
52) Supertype/subtype relationships should be used when the instances of a subtype participate in no relationships which are unique to that subtype.
Answer: FALSE
54) Generalization is a top-down process.
Answer: FALSE
56) The total specialization rule states that an entity instance of a supertype is allowed not to belong to any subtype.
Answer: FALSE
58) When the total specialization rule is set for a supertype/subtype relationship, one could roughly compare the supertype to an abstract class in object-oriented programming.
Answer: FALSE
59) The disjoint rule specifies that if an entity instance of the supertype is a member of one subtype, it MUST simultaneously be a member of another subtype.
Answer: FALSE
66) When subtypes are overlapping, an additional field must be added to the supertype to act as a discriminator.
Answer: FALSE
71) Subtypes at the lowest level of a hierarchy do not inherit attributes from their ancestors.
Answer: FALSE
76) Packaged data models use an entity type to store union data.
Answer: FALSE
78) Packaged data models cause projects to take more time to build.
Answer: FALSE
80) Data models of an existing database are harder for data modelers to read.
Answer: FALSE
82) Creating a data model from a packaged data model requires much more skill than creating one from scratch.
Answer: FALSE
84) Adapting a packaged data model from your DBMS vendor makes it difficult for the application to work with other applications from the same vendor.
Answer: FALSE
86) You will never need to map data in current databases to data in a packaged data model.
Answer: FALSE
53) Specialization is the reverse of generalization.
Answer: TRUE
55) A completeness constraint may specify that each entity of the supertype must be a member of some subtype in the relationship.
Answer: TRUE
60) The overlap rule specifies that if an entity instance of the supertype is a member of one subtype, it can simultaneously be a member of two (or more) subtypes.
Answer: TRUE
68) A subtype can become a supertype if the subtype has other subtypes beneath it.
Answer: TRUE
70) In a supertype/subtype hierarchy, attributes are assigned at the highest logical level that is possible in the hierarchy.
Answer: TRUE
72) Entity clustering is a methodology for grouping one or more entity types and associated relationships into a single abstract entity type.
Answer: TRUE
73) An entity cluster should focus on some area of interest to some community of users, developers or managers.
Answer: TRUE
74) 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.
Answer: TRUE
75) Packaged data models are meant to be customized.
Answer: TRUE
77) A universal data model is a generic or template data model that can be reused as a starting point for a data modeling project.
Answer: TRUE
79) Packaged data models can be developed using proven components.
Answer: TRUE
81) Packaged data models are as flexible as possible because all supertype/subtype relationships allow the total specialization and overlap rules.
Answer: TRUE
83) It is easier t o share information across organizations if companies in the same industry use the same universal data model as the basis for their organizational databases.
Answer: TRUE
85) Because a purchased data model is extensive, you begin by identifying the parts of the data model that apply to your data modeling situation.
Answer: TRUE
87) Mapping existing data to new data in a packaged data model is useful for developing migration plans.
Answer: TRUE
88) It is easy to miss the opportunity to visualize future requirements shown in the full data model when using a packaged data model.
Answer: TRUE
A member of a subtype does NOT necessarily have to be a member of the supertype.
FALSE
A subtype is a generic entity that has a relationship with one or more entities at a lower level.
FALSE
An entity cluster is:
a set of one or more entity types and associated relationships grouped into a single abstract entity type.
An entity cluster can be formed by:
all of the above.
The property by which subtype entities possess the values of all attributes of a supertype is called:
attribute inheritance.
A ________ constraint is a type of constraint that addresses whether an instance of a supertype must also be an instance of at least one subtype.
completeness
A good method for identifying inconsistencies and finding hidden meaning in the customized purchased data model is:
data profiling.
The most important challenge of customizing a purchased data model is:
determining the business rules that will be established through the data model.
The ________ rule specifies that an entity can be a member of only one subtype at a time.
disjoint
A ________ addresses whether an instance of a supertype may simultaneously be a member of two or more subtypes.
disjointedness constraint
When identifying with the parts of the packaged data model that apply to your organization, you should first start with:
entities.
Using a packaged data model, projects take less time and cost because:
essential components and structures are already defined.
The process of defining a more general entity type from a set of more specialized entity types is called:
generalization.
The third step in the data modeling process with a packaged data model is:
map data to be used from package to data in current databases.
