The entity supertype contains common characteristics, and the entity subtypes each contain their own unique characteristics. (T/F) True Entity supertypes and subtypes are organized in a specialization hierarchy.(T/F) True The relationships depicted within the specialization hierarchy are sometimes described in terms of "is-a" relationships.(T/F) True Within a specialization hierarchy, a supertype can exist only within the context of a subtype.(T/F) False One important inheritance characteristic is that all entity subtypes inherit their primary key attribute from their supertype(T/F) True A subtype contains attributes that are common to all of its supertypes.(T/F) False At the implementation level, the supertype and its subtype(s) depicted in the specialization hierarchy maintain a 1:1 relationship.(T/F) True Entity subtypes do not inherit the relationships in which the supertype entity participates.(T/F) False 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.(T/F) False The property of a subtype discriminator enables an entity supertype to inherit the attributes and relationships of the subtype.(T/F) False An entity supertype can have disjoint or overlapping entity subtypes.(T/F) True Disjoint subtypes are subtypes that contain nonunique subsets of the supertype entity set.(T/F) False Overlapping subtypes are subtypes that contain a unique subset of the supertype entity set.(T/F) False Implementing overlapping subtypes requires the use of one discriminator attribute for each subtype. (T/F) True Implementing nonoverlapping subtypes requires the use of one discriminator attribute for each subtype.(T/F) False The completeness constraint can be partial or total.(T/F) True Specialization is the top-down process of identifying lower-level, more specific entity subtypes from a higher-level entity supertype.(T/F) True Generalization is based on grouping unique characteristics and relationships of the subtypes.(T/F) False An entity cluster is a "virtual" entity type used to represent multiple entities and relationships in the ERD.(T/F) True The function of the primary key is to describe an entity. (T/F) False . To model time-variant data, one must create a new entity in an M:N relationship with the original entity.(T/F) False 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.(T/F) True Some designs use redundant relationships as a way to simplify the design.(T/F) True The extended entity relationship model (EERM) is sometimes referred to as the _____. a. c. enhanced entity relationship model _____ is a generic entity type that is related to one or more entity subtypes. a. c. An entity supertype The _____ depicts the arrangement of higher-level entity supertypes (parent entities) and lower-level entity subtypes (child entities). a. c. specialization hierarchy Within a specialization hierarchy, every subtype can have _____ supertype(s) to which it is directly related. a. c. only one A specialization hierarchy can have _____ level(s) of supertype/subtype relationships. a. c. many The property of _____ enables an entity subtype to inherit the attributes and relationships of the supertype. a. c. inheritance One important inheritance characteristic is that all entity subtypes inherit their _____ key attribute from their supertype. a. c. primary At the implementation level, the supertype and its subtype(s) depicted in a specialization hierarchy maintain a(n) _____ relationship. a. c. 1:1 A(n) _____ is the attribute in the supertype entity that determines to which entity subtype each supertype occurrence is related. a. c. subtype discriminator The default comparison condition for the subtype discriminator attribute is the _____ comparison. a. c. equality Which of the following is a specialization hierarchy disjoint constraint scenario in case of partial completeness?
a. b. c. d. Subtype discriminator can be null Which of the following is a specialization hierarchy overlapping constraint scenario in case of partial completeness? a.
b. c. d. Supertype has optional subtypes Nonoverlapping subtypes are subtypes that contain a(n) _____ subset of the supertype entity set. a. c. unique Overlapping subtypes are subtypes that contain _____ subsets of the supertype entity set. a. c. nonunique A total completeness constraint is represented by _____. a. b. c. d. a double horizontal line under a circle A partial completeness constraint is represented by _____. a. c. a single horizontal line under a circle In the context of total completeness, in a(n) _____, every supertype occurrence is a member of only one subtype. a. b. c. d. disjoint constraint In the context of total completeness, in a(n) _____, every supertype occurrence is a member of at least one subtype. a. b. c. d. overlapping constraint _____ is the bottom-up process of identifying a higher-level, more generic entity supertype from lower-level entity subtypes. a. c.
Generalization The purpose of a(n) _____ is to simplify an entity-relationship diagram (ERD) and thus enhance its readability. a. b. c. d. entity cluster An entity cluster is formed by combining multiple interrelated entities into _____. a. c. a single abstract entity object The most important characteristic of an entity is its _____ key, used to uniquely identify each entity instance. a. c. primary A _____ key is a real-world, generally accepted identifier used to uniquely identify real-world objects. a. c. natural If one exists, a data modeler uses a _____ as the primary key of the entity being modeled. a. c. natural identifier A _____ is a primary key created by a database designer to simplify the identification of entity instances. a. b. c. d. surrogate key A primary key's main function is to uniquely identify a(n) _____ within a table. a. c. entity instance or row Composite primary keys are particularly useful as identifiers of composite entities, where each primary key combination is allowed only once in the _____ relationship. M:N The "_____" characteristic of a primary key states that the primary key must uniquely identify each entity instance, must be able to guarantee unique values, and must not contain nulls. a. c. unique values The "_____" characteristic of a primary key states that the selected primary key must not be composed of any attribute(s) that might be considered a violation. a. c. security-compliant According to the "preferably single-attribute" characteristic of a primary key, the primary key: a. b. c. d. should have the minimum number of attributes possible. The "_____" characteristic of a primary key states that the primary key should not have embedded semantic meaning. a. c. nonintelligent Surrogate primary keys are especially helpful when there is no _____ key. a. c. natural _____ keys work with primary keys to properly implement relationships in the relational model. a. c. Foreign The preferred placement for a foreign key when working with a 1:1 relationship is to _____. a. b. c. d. place the foreign key in one of the entities 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 _____. a. b. c. d. one side is mandatory and the other side is optional _____ data refer to data whose values change over time and for which one must keep a history of the data changes. a. c.
Time-variant A _____ occurs when there is one entity in two 1:M relationships to other entities, thus producing an association among the other entities that is not expressed in the model. a. c. fan trap _____ relationships occur when there are multiple relationship paths between related entities. a. c. Redundant The _____ is the result of adding more semantic constructs to the original entity relationship (ER) model. EERM Disjoint subtypes are also known as _____ subtypes. non-overlapping Subtypes that contain nonunique subsets of the supertype entity set are known as _____ subtypes. overlapping The _____ specifies whether each entity supertype occurrence must also be a member of at least one subtype. completeness constraint _____ completeness means that not every supertype occurrence is a member of a subtype. Partial _____ completeness means that every supertype occurrence must be a member of at least one subtype. Total Specialization is based on grouping _____ characteristics and relationships of the subtypes. unique An entity cluster is considered "virtual" or "_____" in the sense that it is not actually an entity in the final ERD. abstract Usually, a data modeler uses a natural identifier as the _____ of the entity being modeled, assuming that the entity has a natural identifier. primary key Unique values can be better managed when they are _____, because the database can use internal routines to implement a counter-style attribute that automatically increments values with the addition of each new row. numeric Composite primary keys are particularly useful as identifiers of composite entities, where each primary key combination is allowed _____ in the M:N relationship. once Composite keys are useful as identifiers of weak entities, where the weak entity has a strong _____ relationship with the parent entity. identifying A weak-entity in a strong identifying relationship with a parent entity is normally used to represent a(n) _____ that is represented in the data model as two separate entities. real-world object One practical advantage of a(n) _____ key is that because it has no intrinsic meaning, values for it can be generated by the DBMS to ensure that unique values are always provided. surrogate While using a surrogate key, one must ensure that the candidate key of the entity in question performs properly through the use of the "_____" and "not null" constraints. unique index From a data modeling point of view, _____ data refer to data whose values change over time and for which one must keep a history of the data changes. time-variant A _____ occurs when a relationship is improperly or incompletely identified and is therefore represented in a way that is not consistent with the real world. design trap The main concern with redundant relationships is that they remain _____ across the model. consistent |
_____ completeness means that every supertype occurrence must be a member of at least one subtype.
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