Chapter 5 Quiz Flashcards
Which of the following statements describe a fan trap in ERD design?
there is one entity in two 1:M relationships to other entities
When looking into the extended entity relationship model (EERM), which of the following statements is not valid about entity supertypes and subtypes?
The entity subtype contains common characteristics
The primary key is possibly the most essential characteristic of an entity; which of the following is not a desirable characteristic of a primary key?
intelligent
Which of the following statements is not valid when describing entity clustering?
An entity cluster is a permanent entity used to represent multiple entities and relationships, intended to simplify the ERD, and thus enhance its readability
What primary key is created by the database designer to simplify the identification of entity instances?
a surrogate key
In the extended entity-relationship model (EERM), which of the following statements best describes the completeness constraint?
specifies whether each entity supertype occurrence must also be a member of at least one subtype
Which of the following statements best describes the essential characteristic of an entity’s primary key?
to guarantee entity integrity, not to describe
In an extended entity relationship, which of the following statements is not valid about inheritance?
Inheriting the relationships of their supertypes means subtypes cannot have relationships of their own
Which statement from the following describes specialization and generalization?
Specialization is the top-down process of identifying lower-level, more specific entity subtypes from a higher-level entity supertype. Generalization is the bottom-up process of identifying a higher-level, more generic entity supertype from lower-level entity subtypes.
Identify the statement that best defines time-variant data.
data that changes over time; its history of data changes must be maintained
