Database Processing, 14e (Kroenke)
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Chapter 5: Data Modeling with the Entity-Relationship Model
1) A data model is a plan for a database design.
Answer: TRUE
AACSB: Information Technology
Difficulty: Easy
LO: To understand the two-phase data modeling/database design process
Classification: Concept
2) The method of constructing data models used in the text is the extended entity-relationship (ER) model.
Answer: TRUE
AACSB: Information Technology
Difficulty: Easy
LO: To understand the two-phase data modeling/database design process
Classification: Concept
3) An entity is something that users want to track.
Answer: TRUE
AACSB: Information Technology
Difficulty: Easy
LO: To be able to determine entities, attributes, and relationships
Classification: Concept
4) Entities of a given type are grouped into entity classes.
Answer: TRUE
AACSB: Information Technology
Difficulty: Easy
LO: To be able to determine entities, attributes, and relationships
Classification: Concept
5) An entity class is described by the structure of the entities in that class.
Answer: TRUE
Copyright © 2016 Pearson Education, Inc.
AACSB: Information Technology
Difficulty: Moderate
LO: To understand entity-relationship (E-R) diagrams
Classification: Concept
6) An entity instance is an occurrence of a particular entity.
Answer: TRUE
AACSB: Information Technology
Difficulty: Easy
LO: To understand entity-relationship (E-R) diagrams
Classification: Concept
7) An entity instance of an entity class is the representation of a particular entity and is described by the values of the attributes of the entity.
Answer: TRUE
AACSB: Information Technology
Difficulty: Difficult
LO: To understand entity-relationship (E-R) diagrams
Classification: Concept
8) An identifier of an entity instance is one or more attributes that name or identify entity instances.
Answer: TRUE
AACSB: Information Technology
Difficulty: Easy
LO: To be able to create entity identifiers
Classification: Concept
9) A compound identifier is an identifier consisting of two or more attributes.
Answer: FALSE
AACSB: Information Technology
Difficulty: Moderate
LO: To be able to create entity identifiers
Classification: Concept
10) In E-R modeling, an attribute describes the characteristics of an entity.
Answer: TRUE
AACSB: Information Technology
Difficulty: Easy
LO: To be able to determine entities, attributes, and relationships
Classification: Concept
11) In E-R modeling, entities within an entity class may have different attributes.
Answer: FALSE
AACSB: Information Technology
Difficulty: Easy
LO: To understand entity-relationship (E-R) diagrams
Classification: Concept
12) An identifier of an entity instance must consist of one and only one attribute.
Answer: FALSE
AACSB: Information Technology
Difficulty: Moderate
LO: To be able to create entity identifiers
Classification: Concept
13) A composite identifier is defined as a composite attribute that is an identifier.
Answer: FALSE
AACSB: Information Technology
Difficulty: Difficult
LO: To be able to create entity identifiers
Classification: Concept
14) An identifier serves the same role for a table that a key does for an entity.
Answer: FALSE
AACSB: Information Technology
Difficulty: Moderate
LO: To be able to create entity identifiers
Classification: Concept
15) Entities can be associated with one another in relationships.
Answer: TRUE
AACSB: Information Technology
Difficulty: Easy
LO: To understand entity-relationship (E-R) diagrams
Classification: Concept
16) The degree of a relationship is the number of entity classes in the relationship.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To be able to determine entities, attributes, and relationships
Classification: Concept
17) A binary relationship is a relationship between two or more entities.
Answer: FALSE
AACSB: Information Technology
Difficulty: Moderate
LO: To be able to determine entities, attributes, and relationships
Classification: Concept
18) Relationships of degree two are referred to as binary relationships.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand entity-relationship (E-R) diagrams
Classification: Concept
19) E-R modeling recognizes both relationship classes and relationship instances.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand entity-relationship (E-R) diagrams
Classification: Concept
20) In today's E-R models, attributes of relationships are still used.
Answer: FALSE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand entity-relationship (E-R) diagrams
Classification: Concept
21) A single relationship class involves only one entity class.
Answer: FALSE
AACSB: Information Technology
Difficulty: Difficult
LO: To be able to determine entities, attributes, and relationships
Classification: Concept
22) A binary relationship is a relationship based on numerical entity instance identifiers.
Answer: FALSE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand entity-relationship (E-R) diagrams
Classification: Concept
23) The degree of a relationship is expressed as the relationship's maximum cardinality.
Answer: FALSE
AACSB: Information Technology
Difficulty: Difficult
LO: To understand entity-relationship (E-R) diagrams
Classification: Concept
24) When transforming a data model into a relational design, relationships of all degrees are treated as combinations of binary relationships.
Answer: TRUE
AACSB: Information Technology; Application of Knowledge
Difficulty: Moderate
LO: To understand the two-phase data modeling/database design process
Classification: Concept
25) The principal difference between an entity and a table is that you can express a relationship between entities without using foreign keys.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand the two-phase data modeling/database design process
Classification: Concept
26) When designing a database, first identify the entities, then determine the attributes, and finally create the relationships.
Answer: FALSE
AACSB: Information Technology; Application of Knowledge
Difficulty: Difficult
LO: To be able to determine entities, attributes, and relationships
Classification: Concept
27) The notation 1:N shows a relationship's maximum cardinalities.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To be able to determine minimum and maximum cardinalities
Classification: Concept
28) Relationships are classified by their cardinality.
Answer: TRUE
AACSB: Information Technology
Difficulty: Easy
LO: To be able to determine minimum and maximum cardinalities
Classification: Concept
29) A relationship's maximum cardinality indicates the maximum number of entities that can participate in the relationship.
Answer: FALSE
AACSB: Information Technology
Difficulty: Difficult
LO: To be able to determine minimum and maximum cardinalities
Classification: Concept
30) In an E-R model, the three types of maximum cardinality are 1:1, 1:N, and N:M.
Answer: TRUE
AACSB: Information Technology
Difficulty: Easy
LO: To be able to determine minimum and maximum cardinalities
Classification: Concept
31) In a 1:N relationship, the term parent refers to the N side of the relationship.
Answer: FALSE
AACSB: Information Technology
Difficulty: Moderate
LO: To be able to determine minimum and maximum cardinalities
Classification: Concept
32) In a 1:N relationship, the parent entity is on the one side of the relationship, and the child entity is on the many side of the relationship.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To be able to determine minimum and maximum cardinalities
Classification: Concept
33) An entity's minimum cardinality in a relationship indicates the number of entity instances that must participate in the relationship.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To be able to determine minimum and maximum cardinalities
Classification: Concept
34) An entity's minimum cardinality in a relationship indicates whether or not an entity must participate in the relationship.
Answer: TRUE
AACSB: Information Technology
Difficulty: Easy
LO: To be able to determine minimum and maximum cardinalities
Classification: Concept
35) In an E-R model, the three types of minimum cardinality are mandatory, optional, and indeterminate.
Answer: FALSE
AACSB: Information Technology
Difficulty: Easy
LO: To be able to determine minimum and maximum cardinalities
Classification: Concept
36) An entity that represents something that can exist on its own is called a strong entity.
Answer: TRUE
AACSB: Information Technology
Difficulty: Easy
LO: To be able to determine entities, attributes, and relationships
Classification: Concept
37) E-R models use an identifying relationship to connect entities that are ID-dependent.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use ID-dependent and other weak entities
Classification: Concept
38) An ID-dependent entity is an entity whose identifier includes the identifier of another entity.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use ID-dependent and other weak entities
Classification: Concept
39) ID-dependent entities are associated by a nonidentifying relationship.
Answer: FALSE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use ID-dependent and other weak entities
Classification: Concept
40) A weak entity is an entity that cannot exist in the database without (and is logically dependent upon) another type of entity also existing in the database.
Answer: TRUE
AACSB: Information Technology
Difficulty: Difficult
LO: To understand and be able to use ID-dependent and other weak entities
Classification: Concept
41) ID-dependent entities are a common type of weak entity.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use ID-dependent and other weak entities
Classification: Concept
42) All weak entities must have a minimum cardinality of 1 on the entity on which it depends.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use ID-dependent and other weak entities
Classification: Concept
43) Subtype entities contain, apart from the identifier, only attributes that do not appear in the supertype.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use supertype/subtype entities
Classification: Concept
44) An attribute that determines which subtype is appropriate is called a discriminator.
Answer: TRUE
AACSB: Information Technology
Difficulty: Easy
LO: To understand and be able to use supertype/subtype entities
Classification: Concept
45) An exclusive subtype pattern has one supertype entity that relates to one or more subtype entities.
Answer: FALSE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use supertype/subtype entities
Classification: Concept
46) Entities with an IS-A relationship should have the same identifier.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use supertype/subtype entities
Classification: Concept
47) One example of a database design using an ID-dependent relationship is the association pattern.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use the ID-dependent association pattern
Classification: Concept
48) One example of a database design using a strong relationship is the multivalued attribute pattern.
Answer: FALSE
AACSB: Information Technology
Difficulty: Difficult
LO: To understand and be able to use the ID-dependent multivalued attribute pattern
Classification: Concept
49) One example of a database design using an ID-dependent relationship is the archetype/instance pattern.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use the ID-dependent archetype/instance pattern
Classification: Concept
50) Data modelers agree that weak, non-ID-dependent entities exist and are important.
Answer: FALSE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use ID-dependent and other weak entities
Classification: Concept
51) Entities containing multivalued attributes are often represented using subtypes.
Answer: FALSE
AACSB: Information Technology
Difficulty: Difficult
LO: To understand and be able to use supertype/subtype entities
Classification: Concept
52) The supremetype entity contains the attributes that are common to all subtypes.
Answer: FALSE
AACSB: Information Technology
Difficulty: Easy
LO: To understand and be able to use supertype/subtype entities
Classification: Concept
53) An attribute that determines which subtype is appropriate is called a discriminator.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use supertype/subtype entities
Classification: Concept
54) Subtypes can be exclusive or inclusive.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use supertype/subtype entities
Classification: Concept
55) Relationships between supertypes and subtypes are called IS-A relationships.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use supertype/subtype entities
Classification: Concept
56) Relationships among instances of a single entity class are called redundant relationships.
Answer: FALSE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use recursive patterns
Classification: Concept
57) There are three types of recursive relationships: 1:1, 1:N, and N:M.
Answer: TRUE
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use recursive patterns
Classification: Concept
58) Recursive relationships only exist for one-to-one relationships.
Answer: FALSE
AACSB: Information Technology
Difficulty: Easy
LO: To understand and be able to use recursive patterns
Classification: Concept
59) Which of the following is not a good reason for designing a data model?
A) It's easier to change things in the data model than it is in the actual DBMS.
B) The data model provides a simplified view of the database that can be shown to people who don't need to see all the details.
C) Creating a data model will help you understand the application area better.
D) The data model can be discarded after the database is operational.
Answer: D
AACSB: Information Technology; Analytical Thinking
Difficulty: Moderate
LO: To understand the purpose of the data modeling process
Classification: Concept
60) Which of the following is not a key element of an E-R model?
A) Relationships
B) Entities
C) Objects
D) Attributes
Answer: C
AACSB: Information Technology
Difficulty: Moderate
LO: To understand entity-relationship (E-R) diagrams
Classification: Concept
61) Entities of a given type are grouped into an ________.
A) entity class
B) entity relationship
C) entity instance
D) entity attribute
Answer: A
AACSB: Information Technology
Difficulty: Easy
LO: To understand entity-relationship (E-R) diagrams
Classification: Concept
62) An occurrence of a particular entity is called an ________.
A) entity class
B) entity relationship
C) entity instance
D) entity attribute
Answer: C
AACSB: Information Technology
Difficulty: Moderate
LO: To understand entity-relationship (E-R) diagrams
Classification: Concept
63) The characteristics of a thing are described by its ________.
A) identifiers
B) entities
C) objects
D) attributes
Answer: D
AACSB: Information Technology
Difficulty: Easy
LO: To be able to determine entities, attributes, and relationships
Classification: Concept
64) Attributes may be ________.
A) complete
B) optional
C) multivalued
D) required
Answer: C
AACSB: Information Technology
Difficulty: Moderate
LO: To be able to determine entities, attributes, and relationships
Classification: Concept
65) An identifier may be ________.
A) composite
B) optional
C) a relationship
D) minimal
Answer: A
AACSB: Information Technology
Difficulty: Easy
LO: To be able to create entity identifiers
Classification: Concept
66) A composite attribute is an attribute that ________.
A) is multivalued
B) describes a characteristic of the relationship
C) consists of a group of attributes
D) is calculated at run-time
Answer: C
AACSB: Information Technology
Difficulty: Moderate
LO: To be able to determine entities, attributes, and relationships
Classification: Concept
67) For a relationship to be considered a binary relationship it must satisfy which of the following conditions?
A) It must involve exactly two entity classes.
B) It must have a maximum cardinality of 1:1.
C) It must have a maximum cardinality of 1:N.
D) Both A and B are correct
Answer: A
AACSB: Information Technology
Difficulty: Difficult
LO: To be able to determine entities, attributes, and relationships
Classification: Concept
68) Which of the following is not a common variant of the E-R model?
A) IE Crow's Foot
B) IDEF1X
C) UML
D) Object-oriented
Answer: D
AACSB: Information Technology
Difficulty: Easy
LO: To understand variations of the E-R model
Classification: Concept
69) Maximum cardinality refers to ________.
A) the most instances of one entity class that can be involved in a relationship instance with another entity class
B) the minimum number of entity classes involved in a relationship
C) whether or not an instance of one entity class is required to be related to an instance of another entity class
D) whether or not an entity is a weak entity
Answer: A
AACSB: Information Technology
Difficulty: Moderate
LO: To be able to determine minimum and maximum cardinalities
Classification: Concept
70) You are given an E-R diagram with two entities, ORDER and CUSTOMER, as shown above, and are asked to draw the relationship between them. If a given customer can place only one order and a given order can be placed by at most one customer, which of the following should be indicated in the relationship symbol between the two entities?
A) N:M
B) 1:1
C) 1:N
D) N:1
Answer: B
AACSB: Information Technology; Application of Knowledge
Difficulty: Moderate
LO: To be able to determine minimum and maximum cardinalities; To understand and be able to use strong entity patterns
Classification: Application
71) You are given an E-R diagram with two entities, ORDER and CUSTOMER, as shown above, and are asked to draw the relationship between them. If a given customer can place many orders and a given order can be placed by at most one customer, which of the following should be indicated in the relationship symbol between the two entities?
A) N:M
B) 1:1
C) 1:N
D) N:1
Answer: D
AACSB: Information Technology; Application of Knowledge
Difficulty: Difficult
LO: To be able to determine minimum and maximum cardinalities; To understand and be able to use strong entity patterns
Classification: Application
72) You are given an E-R diagram with two entities, ORDER and CUSTOMER, as shown above, and are asked to draw the relationship between them. If a given customer can place many orders and a given order can be placed by one or more customers, which of the following should be indicated in the relationship symbol between the two entities?
A) N:M
B) 1:1
C) 1:N
D) N:1
Answer: A
AACSB: Information Technology; Application of Knowledge
Difficulty: Moderate
LO: To be able to determine minimum and maximum cardinalities; To understand and be able to use strong entity patterns
Classification: Application
73) Minimum cardinality refers to ________.
A) the most instances of one entity class that can be involved in a relationship with one instance of another entity class
B) the minimum number of entity classes involved in a relationship
C) whether or not an instance of one entity class is required to be related to an instance of another entity class
D) whether or not an entity is a weak entity
Answer: C
AACSB: Information Technology
Difficulty: Moderate
LO: To be able to determine minimum and maximum cardinalities
Classification: Concept
74) In a minimum cardinality, minimums are generally stated as ________.
A) 0 or 1
B) 1 or N
C) M or N
D) one or many
Answer: A
AACSB: Information Technology
Difficulty: Easy
LO: To be able to determine minimum and maximum cardinalities
Classification: Concept
75) A hash mark across the relationship line near an entity indicates ________.
A) a maximum cardinality of "zero"
B) a maximum cardinality of "one"
C) a minimum cardinality of "optional"
D) a minimum cardinality of "required"
Answer: D
AACSB: Information Technology
Difficulty: Moderate
LO: To be able to determine minimum and maximum cardinalities
Classification: Concept
76) A circle across the relationship line near an entity indicates ________.
A) a maximum cardinality of "zero"
B) a maximum cardinality of "one"
C) a minimum cardinality of "optional"
D) a minimum cardinality of "required"
Answer: C
AACSB: Information Technology
Difficulty: Moderate
LO: To be able to determine minimum and maximum cardinalities
Classification: Concept
77) You are given an E-R diagram with two entities, ORDER and CUSTOMER, as shown above. What does the symbol next to the ORDER entity indicate?
A) A maximum cardinality of "zero"
B) A maximum cardinality of "one"
C) A minimum cardinality of "optional"
D) A minimum cardinality of "required"
Answer: C
AACSB: Information Technology; Application of Knowledge
Difficulty: Moderate
LO: To be able to determine minimum and maximum cardinalities; To understand and be able to use strong entity patterns
Classification: Application
78) You are given an E-R diagram with two entities, ORDER and CUSTOMER, as shown above. What does the symbol next to the CUSTOMER entity indicate?
A) A maximum cardinality of "zero"
B) A maximum cardinality of "one"
C) A minimum cardinality of "optional"
D) A minimum cardinality of "required"
Answer: D
AACSB: Information Technology; Application of Knowledge
Difficulty: Moderate
LO: To be able to determine minimum and maximum cardinalities; To understand and be able to use strong entity patterns
Classification: Application
79) An entity whose identifier includes the identifier of another entity is a(n) ________.
A) strong entity
B) weak entity
C) optional entity
D) required entity
Answer: B
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use ID-dependent and other weak entities; To be able to create entity identifiers
Classification: Concept
80) An entity whose existence depends on the presence of another entity but whose identifier does not include the identifier of the other entity is a(n) ________.
A) strong entity
B) weak entity
C) ID-dependent entity
D) subtype entity
Answer: B
AACSB: Information Technology
Difficulty: Difficult
LO: To understand and be able to use ID-dependent and other weak entities
Classification: Concept
81) Which of the following is considered to be a weak entity?
A) A subtype entity
B) The archetype in an archetype/instance pattern
C) The association entity in an association pattern
D) The parent entity in a parent-child relationship
Answer: C
AACSB: Information Technology
Difficulty: Difficult
LO: To understand and be able to use ID-dependent and other weak entities
Classification: Concept
82) An entity that holds specialized attributes that distinguish it from one or more other similar entities is a ________.
A) supertype
B) subtype
C) discriminator
D) parent
Answer: B
AACSB: Information Technology
Difficulty: Easy
LO: To understand and be able to use supertype/subtype entities
Classification: Concept
83) Which of the following is not true about subtype entities?
A) Subtypes may be exclusive.
B) The supertype and subtypes will have the same identifier.
C) Subtypes are used to avoid a situation in which some attributes are required to be null.
D) All subtypes of a supertype must have the same attributes.
Answer: D
AACSB: Information Technology
Difficulty: Difficult
LO: To understand and be able to use supertype/subtype entities
Classification: Concept
84) An attribute that determines which subtype should be used is a(n) ________.
A) supertype
B) subtype
C) discriminator
D) identifier
Answer: C
AACSB: Information Technology
Difficulty: Easy
LO: To understand and be able to use supertype/subtype entities
Classification: Concept
85) Discriminators can be ________.
A) attributes
B) entities
C) relationships
D) subtypes
Answer: A
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use supertype/subtype entities
Classification: Concept
86) Supertype/subtype entities are said to have a(n) ________ relationship.
A) HAS-A
B) IS-A
C) recursive
D) redundant
Answer: B
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use supertype/subtype entities
Classification: Concept
87) To represent an association pattern in an E-R model, ________.
A) create a new ID-dependent entity with a 1:1 relationship to one other entity
B) create a new weak, but not ID-dependent entity with a 1:1 relationship to one other entity
C) create a new strong entity with a 1:1 relationship to one other entity
D) create a new ID-dependent entity with a N:1 relationships to two parent entities
Answer: D
AACSB: Information Technology; Application of Knowledge
Difficulty: Difficult
LO: To understand and be able to use the ID-dependent association pattern
Classification: Concept
88) To represent a multivalued attribute in an E-R model, ________.
A) create a new ID-dependent entity with a 1:N relationship
B) create a new weak, but not ID-dependent entity with a 1:N relationship
C) create a new strong entity with a 1:1 relationship
D) create a new ID-dependent entity with a 1:1 relationship
Answer: A
AACSB: Information Technology; Application of Knowledge
Difficulty: Difficult
LO: To understand and be able to use the ID-dependent association pattern
Classification: Concept
89) To represent an archetype/instance pattern in an E-R model, ________.
A) create a new ID-dependent entity with a 1:N relationship
B) create a new weak, but not ID-dependent entity with a 1:N relationship
C) create a new strong entity with a 1:1 relationship
D) create a new ID-dependent entity with a 1:1 relationship
Answer: A
AACSB: Information Technology; Application of Knowledge
Difficulty: Difficult
LO: To understand and be able to use the ID-dependent association pattern
Classification: Concept
90) A line-item pattern must involve what kind of entity?
A) Strong entity
B) Supertype entity
C) Weak entity with one identifying relationship
D) Weak entity with two identifying relationships
Answer: C
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use the line-item pattern
Classification: Concept
91) A for-use-by pattern must involve what kind of entity?
A) Strong entity
B) Supertype entity
C) Weak entity with one identifying relationship
D) Weak entity with two identifying relationships
Answer: B
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use the for-use-by pattern
Classification: Concept
92) When an entity has a relationship to itself, we have a(n) ________.
A) supertype/subtype relationship
B) archetype/instance relationship
C) recursive relationship
D) Both A and C are correct
Answer: C
AACSB: Information Technology
Difficulty: Easy
LO: To understand and be able to use recursive patterns
Classification: Concept
93) Recursive relationships can have all of the following maximum cardinalities except ________.
A) 1:1
B) 1:N
C) N:M
D) M:M
Answer: D
AACSB: Information Technology
Difficulty: Moderate
LO: To understand and be able to use recursive patterns
Classification: Concept
94) Suppose you have created a data model for an airline based on a variety of forms, reports, user interviews, data sources, etc. Your client comes forward with a new desired report that includes passenger weights and a relationship between passengers and employees, neither of which is in your E-R diagram. You should ________.
A) create a new, separate E-R diagram with just the new information
B) add the relationship and the weight attribute to the existing data model
C) add the relationship but not the weight attribute
D) add the weight attribute but not the relationship
Answer: B
AACSB: Information Technology; Application of Knowledge
Difficulty: Moderate
LO: To understand the iterative nature of the data modeling process
Classification: Application
95) Describe and discuss the main elements of the Entity-Relationship (E-R) model. Include an example.
Answer: The E-R model is basically made up of entities, attributes and relationships. Entities represent the things people want to keep track of, such as customers and products. Each "thing" is presented by an entity or entity class in this case CUSTOMER and PRODUCT. Individual members of each entity class are called entity instances for example CUSTOMER John Smith and PRODUCT Canned Tomato Soup. Each entity is described by a set of attributes. For example, a CUSTOMER will have a CustomerNumber, a LastName and a FirstName, while a PRODUCT will have a ProductNumber and a Description. These, of course, have specific values for each entity instance. Finally, the entities are connected by relationships. There are relationship classes between entity classes and relationship instances between entity instances. For example, in general a CUSTOMER buys a PRODUCT, and a PRODUCT is sold to a CUSTOMER. Specifically, CUSTOMER John Smith buys a PRODUCT Canned Tomato Soup.
AACSB: Information Technology; Application of Knowledge
Difficulty: Moderate
LO: To be able to determine entities, attributes, and relationships
Classification: Application
96) Distinguish between an entity class and an entity instance.
Answer: An entity class is the collection of all entities of a given type. The entity class is described by the structure of the entities in that class. An entity instance is a representation of a particular entity within the entity class. The entity instance is described by the values of the attributes of the entity. An entity class, then, is a collection containing many entity instances.
AACSB: Information Technology
Difficulty: Moderate
LO: To understand entity-relationship (E-R) diagrams
Classification: Concept
97) What is meant by the degree of a relationship?
Answer: In the E-R model, the degree of a relationship indicates how many entity classes are participating in the relationship. If two entity classes are in the relationship, then the relationship is said to be of degree two and is called a binary relationship. If three entity classes are in the relationship, then the relationship is said to be of degree three and is called a ternary relationship. So, for example, if we have the entity classes CUSTOMER and PRODUCT in a relationship, then they will have a relationship of degree two a binary relationship.
AACSB: Information Technology
Difficulty: Easy
LO: To understand entity-relationship (E-R) diagrams
Classification: Concept
98) What is meant by the cardinality of a relationship?
Answer: In the E-R model, there are two types of cardinality the maximum cardinality and the minimum cardinality. The maximum cardinality is the maximum number of entity instances that can participate in a relationship instance. There are three types of maximum cardinality: one-toone (1:1), one-to-many (1:N) and many-to-many (N:M). The minimum cardinality is the minimum number of entity instances that must participate in a relationship instance. This number is generally zero (0) or one (1). If the number is zero, then participation by that entity instance is optional (O) it does not have to be in a relationship with an instance of the other entity. If the number is one, then participation by that entity instance is mandatory (M) it must participate in a relationship with an instance of the other entity. In a binary relationship there are four (4) possible sets of minimum cardinalities (O-O), (O-M), (M-O) and (M-M).
AACSB: Information Technology
Difficulty: Difficult
LO: To be able to determine minimum and maximum cardinalities
Classification: Concept
99) How is maximum cardinality expressed in IE Crow's Foot E-R diagrams?
Answer: The Crow's Foot E-R diagram notation uses a hash mark to indicate a maximum cardinality of one and a crow's foot to indicate a maximum cardinality of many. Each symbol is placed immediately next to the rectangle symbolizing an entity. These symbols are combined in various forms to signify 1:1, 1:N and N:M relationships.
AACSB: Information Technology
Difficulty: Easy
LO: To understand entity-relationship (E-R) diagrams
Classification: Concept
100) How is minimum cardinality expressed in IE Crow's Foot E-R diagrams?
Answer: The Crow's Foot E-R diagram notation uses a circle to indicate a minimum cardinality of zero (or "optional") and a hash mark to indicate a minimum cardinality of one (or "mandatory"). Each symbol is placed on the relationship line just beyond the symbol indicating maximum cardinality.
AACSB: Information Technology
Difficulty: Easy
LO: To understand entity-relationship (E-R) diagrams
Classification: Concept
101) Distinguish between entity identifiers and keys.
Answer: An entity identifier is an attribute or group of attributes that is used to name or identify instances of an entity class. Unlike a key in the relational model, an entity identifier is more of a logical concept. It is simply an attribute that the users think of as distinguishing between entity instances in their environment.
AACSB: Information Technology; Analytical Thinking
Difficulty: Easy
LO: To be able to create entity identifiers
Classification: Concept
102) What is an ID-Dependent entity? Include an example.
Answer: There are some entities that cannot be completely identified without being associated with another entity that provides additional identifying information. A common example is an apartment, where just the apartment number by itself (for example, the number 12) does not tell you which apartment is being described you have to know which building the apartment is in. Thus the entity APARTMENT needs to be associated with the entity BUILDING. In fact, the entity APARTMENT needs to include the identifier of BUILDING in the identifier of APARTMENT for the identifier of APARTMENT to be complete. An entity that requires the inclusion of another entity's identifier as part of its own composite identifier is called an IDDependent entity.
AACSB: Information Technology; Application of Knowledge
Difficulty: Moderate
LO: To be able to determine entities, attributes, and relationships
Classification: Application
103) Explain the ambiguity in the broad definition of a weak entity.
Answer: The broad definition of a weak entity includes any entity that relies on another entity for its existence in the database. This is ambiguous since this definition can apply to any entity that is involved in a relationship with a minimum cardinality of 1. If the minimum cardinality is 1, then an entity instance in that entity class cannot exist in the database unless there is a related entity instance in the associated entity class. The more restrictive definition of a weak entity indicates that an entity is weak if it logically depends on the other entity for its existence.
AACSB: Information Technology; Analytical Thinking
Difficulty: Difficult
LO: To understand and be able to use ID-dependent and other weak entities
Classification: Concept
104) What are supertype and subtype entities? Include an example.
Answer: When instances of an entity can be categorized into different types with each type sharing some common characteristics while having certain characteristics that are unique to each type, the common attributes can be separated from the unique ones. This is represented in E-R diagrams through the use of supertype and subtype entities. The supertype entity class contains the attributes that are common to all of the subtypes. The subtype entity classes represent the different types, or categories, of the supertype. Only the attributes that are unique to a given subtype tend to be listed as the attributes of that subtype. Each subtype has a relationship with the supertype. All subtypes should have the same identifier as the supertype since they represent different perspectives of the same thing. As an example, consider VEHICLE (VIN, year, make) as a supertype, with subtypes CAR (VIN, model, seatingCapacity) and MOTORCYCLE (VIN, horsepower). All vehicles have VINs, a year, and a make. CARs additionally have a model and a seating capacity and MOTORCYCLES additionally have a horsepower rating.
AACSB: Information Technology; Application of Knowledge
Difficulty: Moderate
LO: To understand and be able to use supertype/subtype entities
Classification: Application