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Exam 5: Advanced Data Modeling

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Question 41

Multiple Choice

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

A) Subtype sets are unique.
B) Supertype has optional subtypes.
C) Subtype discriminators cannot be null.
D) Subtype does not have a supertype.

E) A) and B)
F) All of the above

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Question 42

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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.

A) True
B) False

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Question 43

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

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.

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

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

Explain the "no change over time" characteristic of a primary key.

completeness means that not every supertype occurrence is a member of a subtype.

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

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

When selecting a foreign key placement for a 1:1 relationship, place the PK of the entity on the mandatory side in the entity on the optional side as a FK, and make the FK mandatory when .

Composite keys are useful as identifiers of weak entities, where the weak entity has a strong relationship with the parent entity.

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

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

An entity supertype can have disjoint or overlapping entity subtypes.

A total completeness constraint is represented by .

Some designs use redundant relationships as a way to simplify the design.

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

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

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