Chapter 05 Advanced Data Modeling

Chapter 05: Advanced Data Modeling True / False 1. The entity supertype contains common characteristics, and the entity subtypes each contain their own unique characteristics. a. True b. Fals e ANSWER: True DIFFICULTY: Difficulty: Easy REFERENCES: 5-1a Entity Supertypes and Subtypes LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 2. Entity supertypes and subtypes are organized in a specialization hierarchy. a. True b. Fals e ANSWER: True DIFFICULTY: Difficulty: Easy REFERENCES: 5-1b Specialization Hierarchy LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 3. The relationships depicted within the specialization hierarchy are sometimes described in terms of “is-a” relationships. a. True b. Fals e ANSWER: True DIFFICULTY: Difficulty: Moderate REFERENCES: 5-1b Specialization Hierarchy LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 4. Within a specialization hierarchy, a supertype can exist only within the context of a subtype. a. True b. Fals e ANSWER: False DIFFICULTY: Difficulty: Easy REFERENCES: 5-1b Specialization Hierarchy LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs Page 1 Chapter 05: Advanced Data Modeling 5. One important inheritance characteristic is that all entity subtypes inherit their primary key attribute from their supertype. a. True b. Fals e ANSWER: True DIFFICULTY: Difficulty: Easy REFERENCES: 5-1c Inheritance LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 6. A subtype contains attributes that are common to all of its supertypes. a. True b. Fals e ANSWER: False DIFFICULTY: Difficulty: Moderate REFERENCES: 5-1c Inheritance LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 7. At the implementation level, the supertype and its subtype(s) depicted in the specialization hierarchy maintain a 1:1 relationship. a. True b. Fals e ANSWER: True DIFFICULTY: Difficulty: Easy REFERENCES: 5-1c Inheritance LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 8. Entity subtypes do not inherit the relationships in which the supertype entity participates. a. True b. Fals e ANSWER: False DIFFICULTY: Difficulty: Easy REFERENCES: 5-1c Inheritance LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 9. In specialization hierarchies with multiple levels of supertype and subtypes, a lower-level subtype can inherit only a Page 2 Chapter 05: Advanced Data Modeling few of the attributes and relationships from its upper-level supertypes. a. True b. Fals e ANSWER: False DIFFICULTY: Difficulty: Moderate REFERENCES: 5-1c Inheritance LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 10. The property of a subtype discriminator enables an entity supertype to inherit the attributes and relationships of the subtype. a. True b. Fals e ANSWER: False DIFFICULTY: Difficulty: Easy REFERENCES: 5-1d Subtype Discriminator LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 11. An entity supertype can have disjoint or overlapping entity subtypes. a. True b. Fals e ANSWER: True DIFFICULTY: Difficulty: Easy REFERENCES: 5-1e Disjoint and Overlapping Constraints LEARNING OBJ 05.01 Describe the main extended entity relationship (EER) model constructs and ECTIVES: how they are represented in ERDs and EERDs 12. Disjoint subtypes are subtypes that contain nonunique subsets of the supertype entity set. a. True b. Fals e ANSWER: False DIFFICULTY: Difficulty: Easy REFERENCES: 5-1e Disjoint and Overlapping Constraints LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 13. Overlapping subtypes are subtypes that contain a unique subset of the supertype entity set. a. True Page 3 Chapter 05: Advanced Data Modeling b. Fals e ANSWER: DIFFICULTY: REFERENCES: LEARNING OBJ ECTIVES: False Difficulty: Easy 5-1e Disjoint and Overlapping Constraints 05.01 Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 14. Implementing overlapping subtypes requires the use of one discriminator attribute for each subtype. a. True b. Fals e ANSWER: True DIFFICULTY: Difficulty: Moderate REFERENCES: 5-1e Disjoint and Overlapping Constraints LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 15. The completeness constraint can be partial or total. a. True b. Fals e ANSWER: True DIFFICULTY: Difficulty: Easy REFERENCES: 5-1f Completeness Constraint LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 16. Specialization is the top-down process of identifying lower-level, more specific entity subtypes from a higher-level entity supertype. a. True b. Fals e ANSWER: True DIFFICULTY: Difficulty: Moderate REFERENCES: 5-1g Specialization and Generalization LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 17. An entity cluster is a "virtual" entity type used to represent multiple entities and relationships in the ERD. a. True b. Fals e Page 4 Chapter 05: Advanced Data Modeling ANSWER: True DIFFICULTY: Difficulty: Easy REFERENCES: 5-2 Entity Clustering LEARNING OBJECT05.02 - Use entity clusters to represent multiple entities and relationships in IVES: an entity relationship 18. The function of the primary key is to describe an entity. a. True b. Fals e ANSWER: False DIFFICULTY: Difficulty: Moderate REFERENCES: 5-3b Primary Key Guidelines LEARNING OBJECTIVE05.03 - Describe the characteristics of good primary keys and how to S: select them 19. To model time-variant data, one must create a new entity in an M:N relationship with the original entity. a. True b. Fals e ANSWER: False DIFFICULTY: Difficulty: Moderate REFERENCES: 5-4b Design Case 2: Maintaining History of Time-Variant Data LEARNING OBJECTIVES: 05.04 - Apply flexible solutions for special data-modeling cases 20. 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. True b. Fals e ANSWER: True DIFFICULTY: Difficulty: Easy REFERENCES: 5-4c Design Case 3: Fan Traps LEARNING OBJECTIVES: 05.04 - Apply flexible solutions for special data-modeling cases Multiple Choice 21. The extended entity relationship model (EERM) is sometimes referred to as the _____. a. enclosed entity relationship model b. enhanced entity relationship model d. extended entity relationship c. entity clustering relationship model diagram ANSWER: b DIFFICULTY: Difficulty: Easy REFERENCES: 5-1 The Extended Entity Relationship Model LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and Page 5 Chapter 05: Advanced Data Modeling how they are represented in ERDs and EERDs 22. A(n)_____ is a generic entity type that is related to one or more entity subtypes. a. subtype discriminator b. inheritance d. entity c. specialization hierarchy supertype ANSWER: d DIFFICULTY: Difficulty: Easy REFERENCES: 5-1a Entity Supertypes and Subtypes LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 23. The _____ depicts the arrangement of higher-level entity supertypes (parent entities) and lower-level entity subtypes (child entities). a. subtype discriminator b. inheritance d. entity c. specialization hierarchy supertype ANSWER: c DIFFICULTY: Difficulty: Easy REFERENCES: 5-1b Specialization Hierarchy LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 24. 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 ANSWER: b DIFFICULTY: Difficulty: Moderate REFERENCES: 5-1b Specialization Hierarchy LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 25. A specialization hierarchy can have _____ level(s) of supertype/subtype relationships. a. zero b. only one c. one or many d. many ANSWER: d DIFFICULTY: Difficulty: Easy REFERENCES: 5-1b Specialization Hierarchy LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 26. The property of _____ enables an entity subtype to inherit the attributes and relationships of the supertype. a. subtype discriminator b. inheritance Page 6 Chapter 05: Advanced Data Modeling d. entity c. specialization hierarchy supertype ANSWER: b DIFFICULTY: Difficulty: Easy REFERENCES: 5-1c Inheritance LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 27. One important inheritance characteristic is that all entity subtypes inherit their _____ key attribute from their supertype. b. natural a. primar y c. foreign d. surrogate ANSWER: a DIFFICULTY: Difficulty: Moderate REFERENCES: 5-1c Inheritance LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 28. At the implementation level, the supertype and its subtype(s) depicted in a specialization hierarchy maintain a(n) _____ relationship. b. 1:1 a. selfreferencing c. 1:M d. M:N ANSWER: b DIFFICULTY: Difficulty: Easy REFERENCES: 5-1c Inheritance LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 29. 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 d. entity supertype c. specialization hierarchy ANSWER: a DIFFICULTY: Difficulty: Easy REFERENCES: 5-1d Subtype Discriminator LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 30. The default comparison condition for the subtype discriminator attribute is the _____ comparison. Page 7 Chapter 05: Advanced Data Modeling a. nonequality b. less than d. equality c. greater than ANSWER: d DIFFICULTY: Difficulty:Easy REFERENCES: 5-1d Subtype Discriminator LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 31. 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. ANSWER: a DIFFICULTY: Difficulty: Moderate REFERENCES: 5-1f Completeness Constraint LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 32. 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. ANSWER: b DIFFICULTY: Difficulty: Moderate REFERENCES: 5-1f Completeness Constraint LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 33. Nonoverlapping subtypes are subtypes that contain a(n) _____ subset of the supertype entity set. a. entity b. subtypes c. unique d. nonunique ANSWER: c DIFFICULTY: Difficulty: Easy REFERENCES: 5-1e Disjoint and Overlapping Constraints LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs Page 8 Chapter 05: Advanced Data Modeling 34. Overlapping subtypes are subtypes that contain _____ subsets of the supertype entity set. a. null b. exclusive d. nonunique c. solitar y ANSWER: d DIFFICULTY: Difficulty: Easy REFERENCES: 5-1e Disjoint and Overlapping Constraints LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 35. A total completeness constraint is represented by a _____. a. smaller circle inside a bigger circle b. rhombus inside a circle c. double horizontal line under a circle d. single horizontal line above a circle ANSWER: c DIFFICULTY: Difficulty: Easy REFERENCES: 5-1f Completeness Constraint LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 36. A partial completeness constraint is represented by _____. a. a dotted line b. two dashed lines d. a double horizontal line over a circle c. a single horizontal line under a circle ANSWER: c DIFFICULTY: Difficulty:Easy REFERENCES: 5-1f Completeness Constraint LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 37. 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 ANSWER: d DIFFICULTY: Difficulty: Moderate REFERENCES: 5-1f Completeness Constraint LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs Page 9 Chapter 05: Advanced Data Modeling 38. 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 ANSWER: c DIFFICULTY: Difficulty: Moderate REFERENCES: 5-1f Completeness Constraint LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 39. _____ 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 ANSWER: b DIFFICULTY: Difficulty: Easy REFERENCES: 5-1g Specialization and Generalization LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 40. The purpose of an entity _____ is to simplify an entity-relationship diagram (ERD) and thus enhance its readability. a. constraint b. cluster c. interface d. discriminator ANSWER: b DIFFICULTY: Difficulty: Easy REFERENCES: 5-2 Entity Clustering LEARNING OBJECT05.02 - Use entity clusters to represent multiple entities and relationships in IVES: an entity relationship 41. An entity cluster is formed by combining multiple interrelated entities into _____. b. multiple abstract entity a. a single abstract entity object objects c. a single entity object d. multiple entity objects ANSWER: a DIFFICULTY: Difficulty: Easy REFERENCES: 5-2 Entity Clustering LEARNING OBJECT05.02 - Use entity clusters to represent multiple entities and relationships in IVES: an entity relationship 42. The most important characteristic of an entity is its _____ key, used to uniquely identify each entity instance. b. natural a. primar y Page 10 Chapter 05: Advanced Data Modeling c. foreign d. surrogate ANSWER: a DIFFICULTY: Difficulty: Easy REFERENCES: 5-3 Entity Integrity: Selecting Primary Keys LEARNING OBJECTIVE05.03 - Describe the characteristics of good primary keys and how to S: select them 43. A _____ key is a real-world, generally accepted identifier used to uniquely identify real-world objects. b. natural a. primar y c. foreign d. surrogate ANSWER: b DIFFICULTY: Difficulty: Easy REFERENCES: 5-3a Natural Keys and Primary Keys LEARNING OBJECTIVE05.03 - Describe the characteristics of good primary keys and how to S: select them 44. If one exists, a data modeler uses a _____ as the primary key of the entity being modeled. a. foreign key b. combination key d. natural c. surrogate key identifier ANSWER: d DIFFICULTY: Difficulty: Easy REFERENCES: 5-3a Natural Keys and Primary Keys LEARNING OBJECTIVE05.03 - Describe the characteristics of good primary keys and how to S: select them 45. A _____ is a primary key created by a database designer to simplify the identification of entity instances. b. compound a. composite key key c. natural key d. surrogate key ANSWER: d DIFFICULTY: Difficulty: Easy REFERENCES: 5-3d When to Use Surrogate Primary Keys LEARNING OBJECTIVE05.03 - Describe the characteristics of good primary keys and how to S: select them 46. 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 ANSWER: d DIFFICULTY: Difficulty: Easy REFERENCES: 5-3c When to Use Composite Primary Keys LEARNING OBJECTIVE 05.03 - Describe the characteristics of good primary keys and how to Page 11 Chapter 05: Advanced Data Modeling S: select them 47. 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 d. securityc. preferably singleattribute compliant ANSWER: d DIFFICULTY: Difficulty: Easy REFERENCES: 5-3b Primary Key Guidelines LEARNING OBJECTIVE05.03 - Describe the characteristics of good primary keys and how to S: select them 48. 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 d. securityc. preferably singleattribute complaint ANSWER: a DIFFICULTY: Difficulty: Easy REFERENCES: 5-3b Primary Key Guidelines LEARNING OBJECTIVE05.03 - Describe the characteristics of good primary keys and how to S: select them 49. 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. ANSWER: b DIFFICULTY: Difficulty: Moderate REFERENCES: 5-3b Primary Key Guidelines LEARNING OBJECTIVE05.03 - Describe the characteristics of good primary keys and how to S: select them 50. The “_____” characteristic of a primary key states that the primary key should not have embedded semantic meaning. a. unique values b. nonintelligent d. securityc. preferably singleattribute compliant ANSWER: b DIFFICULTY: Difficulty: Easy REFERENCES: 5-3b Primary Key Guidelines LEARNING OBJECTIVE05.03 - Describe the characteristics of good primary keys and how to S: select them Page 12 Chapter 05: Advanced Data Modeling Completion 51. The _____ is the result of adding more semantic constructs to the original entity relationship (ER) model. ANSWER: extended entity relationship model (EERM) EERM (extended entity relationship model) extended entity relationship model EERM DIFFICULTY: Difficulty: Easy REFERENCES: 5-1 The Extended Entity Relationship Model LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 52. Disjoint subtypes are also known as _____ subtypes. ANSWER: non-overlapping nonoverlapping DIFFICULTY: Difficulty: Easy REFERENCES: 5-1e Disjoint and Overlapping Constraints LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 53. Subtypes that contain nonunique subsets of the supertype entity set are known as _____ subtypes. ANSWER: overlapping DIFFICULTY: Difficulty: Easy REFERENCES: 5-1e Disjoint and Overlapping Constraints LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 54. The _____ specifies whether each entity supertype occurrence must also be a member of at least one subtype. ANSWER: completeness constraint DIFFICULTY: Difficulty: Easy REFERENCES: 5-1f Completeness Constraint LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 55. _____ completeness means that not every supertype occurrence is a member of a subtype. ANSWER: Partial DIFFICULTY: Difficulty: Easy REFERENCES: 5-1f Completeness Constraint LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 56. _____ completeness means that every supertype occurrence must be a member of at least one subtype. ANSWER: Total Page 13 Chapter 05: Advanced Data Modeling DIFFICULTY: REFERENCES: LEARNING OBJ ECTIVES: Difficulty: Easy 5-1f Completeness Constraint 05.01 Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 57. Specialization is based on grouping _____ characteristics and relationships of the subtypes. ANSWER: unique DIFFICULTY: Difficulty: Easy REFERENCES: 5-1g Specialization and Generalization LEARNING OBJ 05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 58. An entity cluster is considered “virtual” or “_____” in the sense that it is not actually an entity in the final ERD. ANSWER: abstract DIFFICULTY: Difficulty: Easy REFERENCES: 5-2 Entity Clustering LEARNING OBJECT05.02 - Use entity clusters to represent multiple entities and relationships in IVES: an entity relationship 59. Usually, a data modeler uses a natural identifier as the _____ of the entity being modeled, assuming that the entity has a natural identifier. ANSWER: primary key DIFFICULTY: Difficulty: Easy REFERENCES: 5-3a Natural Keys and Primary Keys LEARNING OBJECTIVE05.03 - Describe the characteristics of good primary keys and how to S: select them 60. 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. ANSWER: numeric DIFFICULTY: Difficulty: Easy REFERENCES: 5-3b Primary Key Guidelines LEARNING OBJECTIVE05.03 - Describe the characteristics of good primary keys and how to S: select them 61. Composite primary keys are particularly useful as identifiers of composite entities, where each primary key combination is allowed _____ in the M:N relationship. ANSWER: only once once DIFFICULTY: Difficulty: Moderate REFERENCES: 5-3c When to Use Composite Primary Keys LEARNING OBJECTIVE05.03 - Describe the characteristics of good primary keys and how to S: select them 62. Composite keys are useful as identifiers of weak entities, where the weak entity has a strong _____ relationship with the parent entity. Page 14 Chapter 05: Advanced Data Modeling ANSWER: identifying DIFFICULTY: Difficulty: Moderate REFERENCES: 5-3c When to Use Composite Primary Keys LEARNING OBJECTIVE05.03 - Describe the characteristics of good primary keys and how to S: select them 63. 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. ANSWER: real-world object DIFFICULTY: Difficulty: Easy REFERENCES: 5-3c When to Use Composite Primary Keys LEARNING OBJECTIVE05.03 - Describe the characteristics of good primary keys and how to S: select them 64. 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 ANSWER: DIFFICULTY: Difficulty: Easy REFERENCES: 5-3d When to Use Surrogate Primary Keys LEARNING OBJECTIVE05.03 - Describe the characteristics of good primary keys and how to S: select them 65. 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. ANSWER: unique index DIFFICULTY: Difficulty: Moderate REFERENCES: 5-3d When to Use Surrogate Primary Keys LEARNING OBJECTIVE05.03 - Describe the characteristics of good primary keys and how to S: select them 66. 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. ANSWER: time-variant DIFFICULTY: Difficulty: Easy REFERENCES: 5-4b Design Case 2: Maintaining History of Time-Variant Data LEARNING OBJECTIVES: 05.04 - Apply flexible solutions for special data-modeling cases 67. A(n) _____ occurs when a relationship is improperly or incompletely identified and is therefore represented in a way that is not consistent with the real world. ANSWER: design trap DIFFICULTY: Difficulty: Easy REFERENCES: 5-4c Design Case 3: Fan Traps LEARNING OBJECTIVES: 05.04 - Apply flexible solutions for special data-modeling cases 68. The main concern with redundant relationships is that they remain _____ across the model. ANSWER: consistent DIFFICULTY: Difficulty: Moderate Page 15 Chapter 05: Advanced Data Modeling REFERENCES: 5-4d Design Case 4: Redundant Relationships LEARNING OBJECTIVES: 05.04 - Apply flexible solutions for special data-modeling cases 69. _____ keys work with primary keys to properly implement relationships in the relational model. ANSWER: Foreign DIFFICULTY: Difficulty: Easy REFERENCES: 5-4a Design Case 1: Implementing 1:1 Relationships LEARNING OBJECTIVES: 05.04 - Apply flexible solutions for special data-modeling cases 70. A(n) _____ occurs when you have 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. ANSWER: fan trap DIFFICULTY: Difficulty: Moderate REFERENCES: 5-4c Design Case 3: Fan Traps LEARNING OBJECTIVES: 05.04 - Apply flexible solutions for special data-modeling cases Essay 71. What do specialization hierarchies do? ANSWER: Entity supertypes and subtypes are organized in a specialization hierarchy, which depicts the arrangement of higher-level entity supertypes (parent entities) and lower-level entity subtypes (child entities). Specialization hierarchies enable the data model to capture additional semantic content (meaning) into the ERD. A specialization hierarchy provides the means to: • Support attribute inheritance. • Define a special supertype attribute known as the subtype discriminator. • Define disjoint/overlapping constraints and complete/partial constraints. DIFFICULTY: Difficulty: Moderate REFERENCES 5-1b Specialization Hierarchy : LEARNING O 05.01 BJECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 72. Differentiate between specialization and generalization. ANSWER: Specialization is the top-down process of identifying lower-level, more specific entity subtypes from a higher-level entity supertype. Specialization is based on grouping the unique characteristics and relationships of the subtypes. On the other hand, generalization is the bottom-up process of identifying a higher-level, more generic entity supertype from lower-level entity subtypes. Generalization is based on grouping the common characteristics and relationships of the subtypes. DIFFICULTY: Difficulty: Moderate REFERENCES 5-1g Specialization and Generalization : LEARNING O 05.01 BJECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 73. Explain the two criteria that help a designer in determining when to use subtypes and supertypes. Page 16 Chapter 05: Advanced Data Modeling ANSWER: Two criteria help a designer determine when to use subtypes and supertypes: 1. There must be different, identifiable kinds or types of an entity in the user’s environment. 2. The different kinds or types of instances should each have one or more attributes that are unique to that kind or type of instance. DIFFICULTY: Difficulty: Moderate REFERENCES: 5-1a Entity Supertypes and Subtypes LEARNING OBJ05.01 ECTIVES: Describe the main extended entity relationship (EER) model constructs and how they are represented in ERDs and EERDs 74. Explain the “no change over time” characteristic of a primary key. ANSWER: If an attribute has semantic meaning, it might be subject to updates, which is why names do not make good primary keys. If a primary key is subject to change, the foreign key values must be updated, thus adding to the database work load. Furthermore, changing a primary key value means that one is basically changing the identity of an entity. In short, the PK should be permanent and unchangeable. DIFFICULTY: Difficulty: Moderate REFERENCES 5-3b Primary Key Guidelines : LEARNING O 05.03 - Describe the characteristics of good primary keys and how to select them BJECTIVES: 75. In which two cases are composite primary keys particularly useful? ANSWER: Composite primary keys are particularly useful in two cases: 1. As identifiers of composite entities, in which each primary key combination is allowed only once in the M:N relationship. 2. As identifiers of weak entities, in which the weak entity has a strong identifying relationship with the parent entity. DIFFICULTY: Difficulty: Moderate REFERENCES: 5-3c When to Use Composite Primary Keys LEARNING OB 05.03 - Describe the characteristics of good primary keys and how to select them JECTIVES: Page 17