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chapter 6 database
MIS 3140 Data & Process Modeling Oakland University The entity supertype contains common characteristics, and the entity subtypes each contain their own unique characteristics. T/F Entity supertypes and subtypes are organized in a specialization hierarchy. T/F The relationships depicted within the specialization hierarchy are sometimes described in terms of "is-a" relationships. T/F Within a specialization hierarchy, a supertype can exist only within the context of a subtype. T/F One important inheritance characteristic is that all entity subtypes inherit their primary key attribute from their supertype. T/F A subtype contains attributes that are common to all of its supertypes. T/F Entity subtypes do not inherit the relationships in which the supertype entity participates. T/F 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 At the implementation level, the supertype and its subtype(s) depicted in the specialization hierarchy maintain a 1:1 relationship. T/F The property of a subtype discriminator enables an entity supertype to inherit the attributes and relationships of the subtype. T/F An entity supertype can have disjoint or overlapping entity subtypes. T/F Disjoint subtypes are subtypes that contain nonunique subsets of the supertype entity set. T/F Overlapping subtypes are subtypes that contain a unique subset of the supertype entity set. T/F Implementing overlapping subtypes requires the use of one discriminator attribute for each subtype. T/F Implementing nonoverlapping subtypes requires the use of one discriminator attribute for each subtype. T/F The completeness constraint can be partial or total. T/F Specialization is the top-down process of identifying lower-level, more specific entity subtypes from a higher-level entity supertype. T/F Generalization is based on grouping unique characteristics and relationships of the subtypes. T/F An entity cluster is a "virtual" entity type used to represent multiple entities and relationships in the ERD. T/F The function of the primary key is to describe an entity. T/F To model time-variant data, one must create a new entity in an M:N relationship with the original entity. T/F 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 Some designs use redundant relationships as a way to simplify the design. T/F The extended entity relationship model (EERM) is sometimes referred to as the __________. a. enclosed entity relationship model b. enhanced entity relationship model c. entity clustering relationship model d. extended entity relationship diagram b. enhanced entity relationship model __________ is a generic entity type that is related to one or more entity subtypes. a. A subtype discriminator b. Inheritance c. A specialization hierarchy d. An entity supertype The __________ depicts the arrangement of higher-level entity supertypes (parent entities) and lower-level entity subtypes (child entities). a. subtype discriminator b. inheritance c. specialization hierarchy d. entity supertype c. specialization hierarchy Within a specialization hierarchy, every subtype can have __________ supertype(s) to which it is directly related. a. zero b. only one c. one or many d. many A specialization hierarchy can have __________ level(s) of supertype/subtype relationships. a. zero b. only one c. one or many d. many The property of __________ enables an entity subtype to inherit the attributes and relationships of the supertype. a. subtype discriminator b. inheritance c. specialization hierarchy d. entity supertype One important inheritance characteristic is that all entity subtypes inherit their __________ key attribute from their supertype. a. primary b. natural c. foreign d. surrogate At the implementation level, the supertype and its subtype(s) depicted in a specialization hierarchy maintain a(n) __________ relationship. a. self-referencing b. 1:1 c. 1:M d. M:N A(n) __________ is the attribute in the supertype entity that determines to which entity subtype each supertype occurrence is related. a. subtype discriminator b. inheritance discriminator c. specialization hierarchy d. entity supertype The default comparison condition for the subtype discriminator attribute is the __________ comparison. a. nonequality b. less than c. greater than d. equality Which of the following is a specialization hierarchy disjoint constraint scenario in case of partial completeness? a. Subtype discriminator can be null. b. Subtype discriminator cannot be null. c. Each supertype occurrence is a member of only one subtype. d. Each supertype occurrence is a member of at least one subtype. a. Subtype discriminator can be null. 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. b. Supertype has optional subtypes. Nonoverlapping subtypes are subtypes that contain a(n) __________ subset of the supertype entity set. a. entity b. subtypes c. unique d. nonunique Overlapping subtypes are subtypes that contain __________ subsets of the supertype entity set. a. null b. exclusive c. solitary d. nonunique A total completeness constraint is represented by __________. a. a smaller circle inside a bigger circle b. a rhombus inside a circle c. a double horizontal line under a circle d. a single horizontal line above a circle c. a double horizontal line under a circle A partial completeness constraint is represented by __________. a. a dotted line b. two dashed lines c. a single horizontal line under a circle d. a double horizontal line over a circle 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. foreign key constraint b. nonunique constraint c. overlapping constraint d. disjoint constraint In the context of total completeness, in a(n) __________, every supertype occurrence is a member of at least one subtype. a. unique constraint b. disjoint constraint c. overlapping constraint d. foreign key constraint c. overlapping constraint __________ is the bottom-up process of identifying a higher-level, more generic entity supertype from lower-level entity subtypes. a. Specialization b. Generalization c. Normalization d. Total completeness The purpose of a(n) __________ is to simplify an entity-relationship diagram (ERD) and thus enhance its readability. a. entity constraint b. entity cluster c. entity interface d. entity discriminator An entity cluster is formed by combining multiple interrelated entities into __________. a. a single abstract entity object b. multiple abstract entity objects c. a single entity object d. multiple entity objects a. a single abstract entity object The most important characteristic of an entity is its __________ key, used to uniquely identify each entity instance. a. primary b. natural c. foreign d. surrogate A __________ key is a real-world, generally accepted identifier used to uniquely identify real-world objects. a. primary b. natural c. foreign d. surrogate If one exists, a data modeler uses a __________ as the primary key of the entity being modeled. a. foreign key b. combination key c. surrogate key d. natural identifier A __________ is a primary key created by a database designer to simplify the identification of entity instances. a. composite key b. compound key c. natural key d. surrogate key A primary key's main function is to uniquely identify a(n) __________ within a table. a. attribute b. entity instance or row c. entity subtype d. natural key or identifier b. 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. a. 0:1 b. 1:1 c. 1:M d. 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. unique values b. nonintelligent c. preferably single-attribute d. security-complaint 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. unique values b. nonintelligent c. preferably single-attribute d. security-compliant According to the "preferably single-attribute" characteristic of a primary key, the primary key: a. must be able to guarantee unique attribute values. b. should have the minimum number of attributes possible. c. should have embedded semantic meaning associated with each attribute. d. must be composed of attributes that are free from security risks or violations. b. 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. unique values b. nonintelligent c. preferably single-attribute d. security-compliant Surrogate primary keys are especially helpful when there is no __________ key. a. primary b. natural c. foreign d. composite __________ keys work with primary keys to properly implement relationships in the relational model. a. Foreign b. Composite c. Natural d. Surrogate The preferred placement for a foreign key when working with a 1:1 relationship is to __________. a. use the same primary key for both entities b. create a bridge entity c. place the foreign key in one of the entities d. place the surrogate key in both entities c. 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. one side is mandatory and the other side is optional b. one side participates in another relationship c. both sides are optional d. both sides are mandatory a. 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. Time-sensitive b. Time-variant c. Historical d. Change-based 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. surrogate primary key b. time-variant data c. design trap d. fan trap
__________ relationships occur when there are multiple relationship paths between related entities. a. Redundant b. Duplicated c. Time-variant d. Supertype What is the attribute in the supertype entity that determines to which entity subtype each supertype occurrence is related?Cards
Is a generic entity that is related to one or more entity subtypes?A supertype is a generic entity type that has a relationship with one or more subtypes. A subtype is a sub-grouping of the entities in an entity type that is meaningful to the organization and that shares common attributes or relationships distinct from other subgroups.
How many Supertypes can a subtype be directly related to?However, a subtype is (directly) a subtype of only one supertype. Thus, the use of supertypes and subtypes in ERDs resembles the use of ``single inheritance'' between classes, in object-oriented programming.
What type of relationship is established between a supertype and an subtype?6. What type of relationship is established between a supertype and a subtype? Between the supertype and subtype set relation “one to one” or 1:1.
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Is the attribute in the supertype entity that determines to which subtype the supertype occurrence is related?
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