Chapter 5: Data Modeling with the Entity-Relationship Model
88) 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 E) create a new weak, but not ID-dependent entity with a 1:1 relationship
/Answer: A Diff: 3 Page Ref: 201-203
85) Supertype subtype entities are said to have a(n) ________ relationship. A) HAS-A B) IS-A C) recursive D) redundant E) multivalue
/Answer: B Diff: 2 Page Ref: 191-192
49) One example of a database design using an ID-dependent relationship is the archetype instance pattern.
/Answer: TRUE Diff: 2 Page Ref: 196
60) Entities of a given type are grouped into an ________. A) entity class B) entity relationship C) entity instance D) entity attribute E) None of the above.
Answer: A Diff: 1 Page Ref: 181
68) 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 E) None of the above.
Answer: A Diff: 2 Page Ref: 184
66) 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) A and B E) A and C
Answer: A Diff: 3 Page Ref: 182-184
87) 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 E) create a new weak, but not ID-dependent entity with a 1:1 relationship
Answer: A Diff: 3 Page Ref: 199-201
92) 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. Diff: 2 Page Ref: 181
97) 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. Diff: 1 Page Ref: 181-182
81) 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) A and C E) B and C
Answer: B Diff: 1 Page Ref: 191-192
69) 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) 0:1 B) 1:1 C) 1:N D) N:1 E) N:M
Answer: B Diff: 2 Page Ref: 184-185
79) 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) A and C E) B and C
Answer: B Diff: 2 Page Ref: 189-190 Fig 5-12
61) The occurrence of a particular entity is called an ________. A) entity class B) entity relationship C) entity instance D) entity attribute E) None of the above.
Answer: C Diff: 1 Page Ref: 181
65) 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 E) is an identifier
Answer: C Diff: 1 Page Ref: 181-182
83) An attribute that determines which subtype should be used is a ________. A) supertype B) subtype C) discriminator D) A and C E) B and C
Answer: C Diff: 1 Page Ref: 191-192
72) 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 E) None of the above.
Answer: C Diff: 2 Page Ref: 185
75) 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" E) None of the above.
Answer: C Diff: 2 Page Ref: 185-186
76) 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" E) None of the above.
Answer: C Diff: 2 Page Ref: 185-186
59) Which of the following is not a key element of an E-R model? A) Identifiers B) Entities C) Objects D) Attributes E) Relationships
Answer: C Diff: 2 Page Ref: 80-183
62) The characteristics of a thing are described by its ________. A) identifiers B) entities C) objects D) attributes E) relationships
Answer: D Diff: 1 Page Ref: 181
64) An identifier may be ________. A) composite B) a single attribute C) a relationship D) A and B E) A, B, and C
Answer: D Diff: 1 Page Ref: 181-182
84) Discriminators can be ________. A) exclusive only B) inclusive only C) decisive only D) A or B E) B or C
Answer: D Diff: 1 Page Ref: 191-192
63) Attributes may be ________. A) composite B) element C) multivalued D) A and C E) B and C
Answer: D Diff: 2 Page Ref: 181
73) In a minimum cardinality, minimums are generally stated as ________. A) 0 B) 1 C) N D) A or B E) A, B, or C
Answer: D Diff: 2 Page Ref: 185-186
74) 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" E) None of the above.
Answer: D Diff: 2 Page Ref: 185-186
77) 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" E) None of the above.
Answer: D Diff: 2 Page Ref: 185-186
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 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) 0:1 B) 1:1 C) 1:N D) N:1 E) N:M
Answer: D Diff: 3 Page Ref: 184-185
86) 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 1:N relationship to one of two parent entities E) create a new weak, but not ID-dependent entity with a 1:N relationship to one of two parent entities
Answer: D Diff: 3 Page Ref: 196-199
67) Common variants of the E-R model include: A) IE Crow's Foot B) IDEF1X C) UML D) A and B E) A, B, and C
Answer: E Diff: 1 Page Ref: 186-187
90) Recursive relationships can have which of the following maximum cardinalities? A) 1:1 B) 1:N C) N:M D) A or B E) A, B, or C
Answer: E Diff: 1 Page Ref: 207-209
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 one or more customers, which of the following should be indicated in the relationship symbol between the two entities? A) 0:1 B) 1:1 C) 1:N D) N:1 E) N:M
Answer: E Diff: 2 Page Ref: 184-185
78) An entity whose identifier includes the identifier of another entity is a(n) ________. A) strong entity B) weak entity C) ID-dependent entity D) A and C E) B and C
Answer: E Diff: 2 Page Ref: 189-190 Fig 5-12
80) Which of the following is considered to be a weak entity? A) ID-dependent entity B) subtype entity C) association entity D) B and C E) A, B, and C
Answer: E Diff: 2 Page Ref: 189-199
82) 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) Subtypes have attributes that are required by the supertype. E) Subtypes can produce a closer-fitting data model.
Answer: E Diff: 3 Page Ref: 191-192
11) In E-R modeling, entities within an entity class may have different attributes.
Answer: FALSE Diff: 1 Page Ref: 181
12) An identifier of an entity instance must consist of one and only one attribute.
Answer: FALSE Diff: 1 Page Ref: 181-182
35) In an E-R model, the three types of minimum cardinality are mandatory, optional and indeterminate.
Answer: FALSE Diff: 1 Page Ref: 185-186 Fig 5-6
52) The supremetype entity contains the attributes that are common to all subtypes.
Answer: FALSE Diff: 1 Page Ref: 191-192
58) Recursive relationships only exist for one-to-one relationships.
Answer: FALSE Diff: 1 Page Ref: 207-209
14) An identifier serves the same role for a table that a key does for an entity.
Answer: FALSE Diff: 2 Page Ref: 181-182
20) In today's E-R models, attributes of relationships are still used.
Answer: FALSE Diff: 2 Page Ref: 181-182
9) A compound identifier is an identifier consisting of two or more attributes.
Answer: FALSE Diff: 2 Page Ref: 181-182
17) A binary relationship is a relationship between two or more entities.
Answer: FALSE Diff: 2 Page Ref: 183
22) A binary relationship is a relationship based on numerical entity instance identifiers.
Answer: FALSE Diff: 2 Page Ref: 183
31) In a 1:N relationship, the term parent refers to the N side of the relationship.
Answer: FALSE Diff: 2 Page Ref: 184
39) ID-dependent entities are associated by a nonidentifying relationship.
Answer: FALSE Diff: 2 Page Ref: 189-190 Fig 5-12
50) Data modelers agree that weak, non-ID-dependent entities exist and are important.
Answer: FALSE Diff: 2 Page Ref: 191
45) An exclusive subtype pattern has one supertype entity that relates to one or more subtype entities.
Answer: FALSE Diff: 2 Page Ref: 191-192
51) Entities containing optional sets of attributes are often represented using subtypes.
Answer: FALSE Diff: 2 Page Ref: 191-192
48) One example of a database design using a strong relationship is the multivalued attribute pattern.
Answer: FALSE Diff: 2 Page Ref: 196
56) Relationships among instances of a single entity class are called redundant relationships.
Answer: FALSE Diff: 2 Page Ref: 207
13) A composite identifier is defined as a composite attribute that is an identifier.
Answer: FALSE Diff: 3 Page Ref: 181-182
21) A single relationship class involves only one entity class.
Answer: FALSE Diff: 3 Page Ref: 181-182
26) When designing a database, first identify the entities, then determine the attributes, and finally create the relationships.
Answer: FALSE Diff: 3 Page Ref: 183-184
23) The degree of a relationship is expressed as the relationship's maximum cardinality.
Answer: FALSE Diff: 3 Page Ref: 183-185
29) A relationship's maximum cardinality indicates the maximum number of entities that can participate in the relationship.
Answer: FALSE Diff: 3 Page Ref: 184
93) 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. Diff: 1 Page Ref: 183
94) 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-to-one (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). Diff: 3 Page Ref: 184-186
1) A data model is a plan for a database design.
Answer: TRUE
2) The method of constructing data models used in the text is the extended entity-relationship (E-R) model.
Answer: TRUE Diff: 1 Page Ref: 180
10) In E-R modeling, an attribute describes the characteristics of an entity.
Answer: TRUE Diff: 1 Page Ref: 181
3) An entity is something that users want to track.
Answer: TRUE Diff: 1 Page Ref: 181
4) Entities of a given type are grouped into entity classes.
Answer: TRUE Diff: 1 Page Ref: 181
6) An entity instance is the occurrence of a particular entity.
Answer: TRUE Diff: 1 Page Ref: 181
8) An identifier of an entity instance is one or more attributes that name or identify entity instances.
Answer: TRUE Diff: 1 Page Ref: 181
19) E-R modeling recognizes both relationship classes and relationship instances.
Answer: TRUE Diff: 1 Page Ref: 181-182
15) Entities can be associated with one another in relationships.
Answer: TRUE Diff: 1 Page Ref: 182
28) Relationships are classified by their cardinality.
Answer: TRUE Diff: 1 Page Ref: 184
30) In an E-R model, the three types of maximum cardinality are 1:1, 1:N and N:M.
Answer: TRUE Diff: 1 Page Ref: 184-185 Fig 5-5
34) A relationship's minimum cardinality indicates whether or not an entity must participate in the relationship.
Answer: TRUE Diff: 1 Page Ref: 185-186
36) An entity that represents something that can exist on its own is called a strong entity.
Answer: TRUE Diff: 1 Page Ref: 189
44) An attribute that determines which subtype is appropriate is called a discriminator.
Answer: TRUE Diff: 1 Page Ref: 191-192
5) An entity class is described by the structure of the entities in that class.
Answer: TRUE Diff: 2 Page Ref: 181
16) The degree of a relationship is the number of entity classes in the relationship.
Answer: TRUE Diff: 2 Page Ref: 183
18) Relationships of degree two are referred to as binary relationships.
Answer: TRUE Diff: 2 Page Ref: 183
24) When transforming a data model into a relational design, relationships of all degrees are treated as combinations of binary relationships.
Answer: TRUE Diff: 2 Page Ref: 183
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 Diff: 2 Page Ref: 183-184
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 Diff: 2 Page Ref: 184
27) The notation 1:N shows the relationship's maximum cardinality.
Answer: TRUE Diff: 2 Page Ref: 184-185
33) A relationship's minimum cardinality indicates the number of entity instances that must participate in the relationship.
Answer: TRUE Diff: 2 Page Ref: 185-186
37) E-R models use an identifying relationship to connect entities that are ID-dependent.
Answer: TRUE Diff: 2 Page Ref: 189
38) An ID-dependent entity is an entity whose identifier includes the identifier of another entity.
Answer: TRUE Diff: 2 Page Ref: 189-190 Fig 5-12
41) ID-dependent entities are a common type of weak entity.
Answer: TRUE Diff: 2 Page Ref: 189-191 Fig 5-12
54) Subtypes can be exclusive or inclusive.
Answer: TRUE Diff: 2 Page Ref: 191-192
46) Entities with an IS-A relationship should have the same identifier.
Answer: TRUE Diff: 2 Page Ref: 191-192
53) An attribute that determines which subtype is appropriate is called a discriminator.
Answer: TRUE Diff: 2 Page Ref: 191-192
55) Relationships between supertypes and subtypes are called IS-A relationships.
Answer: TRUE Diff: 2 Page Ref: 191-192
47) One example of a database design using an ID-dependent relationship is the association pattern.
Answer: TRUE Diff: 2 Page Ref: 196
57) There are three types of recursive relationships: 1:1, 1:N and N:M.
Answer: TRUE Diff: 2 Page Ref: 207-209
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 Diff: 3 Page Ref: 181
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 Diff: 3 Page Ref: 189-190 Fig 5-12
42) All weak entities must have a minimum cardinality of 1 on the entity on which it depends.
Answer: TRUE Diff: 3 Page Ref: 189-191 Fig 5-12
43) Subtype entities contain only attributes unique to the subtypes.
Answer: TRUE Diff: 3 Page Ref: 191-192
96) 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. Diff: 1 Page Ref: 185-186
95) 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. Diff: 1 Page Ref: 184-185
91) Describe and discuss the main elements of the Entity-Relationship (E-R) model.
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. Diff: 1 Page Ref: 180-184
99) 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. Diff: 3 Page Ref: 189-191 Fig 5-12
98) What is an ID-Dependent entity?
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 ID-Dependent entity. Diff: 2 Page Ref: 189-190
100) What are supertype and subtype entities?
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. Diff: 2 Page Ref: 191-192
89) When an entity has a relationship to itself, we have a(n) ________. A) supertype subtype relationship B) archetype/instance relationship C) recursive relationship D) A or C E) B or C
Diff: 1 Page Ref: 207 /Answer: C