MIST Ch 5

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 following statements describe a fan trap in ERD design? a. A fan trap occurs when there is one entity in two 1:1 relationships to other entities. b. A fan trap occurs when there is one entity in two 1:1 relationships. c. A fan trap occurs when there is one entity in two 1:M relationships to other entities. d. A fan trap occurs when there are more than two entities in 1:M relationships.

A fan trap occurs when there is one entity in two 1:M relationships to other entities.

Which of the following statements is not valid when describing entity clustering? a. An entity cluster is a "virtual" entity type used to represent multiple entities and relationships in the ERD. b. An entity cluster is formed by combining multiple interrelated entities into a single, abstract entity object. c. An entity cluster is a permanent entity used to represent multiple entities and relationships, intended to simplify the ERD, and thus enhance its readability. d. An entity cluster is considered "virtual" or "abstract" because it is not an actual entity in the final ERD.

An entity cluster is a permanent entity used to represent multiple entities and relationships, intended to simplify the ERD, and thus enhance its readability.

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 of the following is an example of a foreign key? a. It uniquely identifies a record in the relational database table. b. It is a combination of UNIQUE and Not Null constraints. c. Its value cannot be deleted from the parent table. d. Its value can be deleted from the child table.

Its value can be deleted from the child table.

Which statement from the following describes specialization and generalization? a. 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. b. Specialization is the top-down process of identifying lower-level, more specific entity supertypes from a higher-level entity subtype. Generalization is the bottom-up process of identifying a higher-level, more generic entity subtype from lower-level entity supertypes. c. Specialization is the top-down process of identifying lower-level, more specific entity supertypes from a higher-level entity subtype. Generalization is the bottom-up process of identifying a higher-level, more generic entity supertype from lower-level entity subtypes.

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.

Which of the following is a specialization hierarchy disjoint constraint scenario, in the case of partial completeness? a. Each supertype occurrence is a member of at least one subtype. b. Subtype discriminator can be null. c. Each supertype occurrence is a member of only one subtype. d. Subtype discriminator cannot be null.

Subtype discriminator can be null.

In the extended entity-relationship model (EERM), which of the following statements best describes the completeness constraint? a. Total completeness constraint means that every subtype occurrence must be a member of at least one supertype. b. The completeness constraint specifies whether each entity supertype occurrence must also be a member of at least one subtype. c. Partial completeness constraint means that every supertype occurrence is a member of a subtype. d. The completeness constraint specifies whether each entity subtype occurrence must also be a member of at least one supertype.

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

When looking into the extended entity relationship model (EERM), which of the following statements is not valid about entity supertypes and subtypes? a. Entity supertype and subtype are based on a hierarchical structure. b. The entity supertype contains common characteristics with subtype. c. The entity subtype contains common characteristics. d. An entity supertype is a generic entity type related to one or more entity subtypes.

The entity subtype contains common characteristics.

Which of the following statements best describes the essential characteristic of an entity's primary key? a. A primary key is the attribute or combination of attributes uniquely identifying an entity's instance in an entity set. b. The main function of the primary key is to guarantee entity integrity and to "describe" the entity. c. The main function of the primary key is to guarantee entity integrity, not to "describe" the entity. d. It has no intrinsic meaning; values for it can be generated by the DBMS to ensure that unique values are always provided.

The main function of the primary key is to guarantee entity integrity, not to "describe" the entity.

Identify the statement that best defines time-variant data. a. Time-variant data refers to data that changes over time; its history of data changes must be maintained. b. Time-variant data refers to data that does not change over time. c. Time-variant data refers to data that was created redundantly. d. Time-variant data refers to data that changes over time, with no history of data change tracking.

Time-variant data refers to data that changes over time; its history of data changes must be maintained.

Which of the answers below is not the most important characteristic of an entity? a. A primary key b. A foreign key c. A single attribute d. Some combination of attributes

a foreign key

What primary key is created by the database designer to simplify the identification of entity instances?

a surrogate key

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

consistent

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

generalization

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? a. Unique value b. Security-compliant c. Intelligent d. No change over time

intelligent

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

natural

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

natural identifier

Which of the answers below is familiar to end users and forms part of their day-to-day business vocabulary? a. A foreign key b. A code key c. A system key d. A natural key

natural key

The surrogate key has __ meaning in the user's environment.

no meaning

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

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

only one

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

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

to avoid the display of attributes