chapter 02 review

Database Processing - Ninth Edition

CHAPTER 2

The Entity Relationship Model

True-False Questions

1. E-R models are expressed using a single standardized set of universally accepted symbols.Answer: False Level: easyPage: 31

2. A schema is a representation of something of interest to the modeler.Answer: True Level: easyPage: 32

3. An internal schema is a representation of how users view the database.Answer: False Level: easyPage: 32

4. A conceptual schema is a complete logical view of the database.Answer: True Level: easyPage: 32

5. An implementational schema shows physical storage using a particular product or technique.Answer: False Level: easyPage: 32

6. An entity is something in the users’ work environment that the users want to track.Answer: True Level: easyPage: 37

7. Entities of a given type are grouped into entity classes.Answer: True Level: easyPage: 37

8. An entity class is described by the structure of the entities in that class.Answer: True Level: moderatePage: 37

9. 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 Level: hardPage: 37

10. In E-R modeling, entities within an entity class may have different attributes.Answer: False Level: easyPage: 37

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Chapter 2 - The Entity Relationship Model

11. In E-R modeling, an attribute may be either composite or multi-value, but it cannot be both.

Answer: False Level: moderatePage: 37

12. An identifier of an entity instance must consist of one and only one attribute.Answer: False Level: easyPage: 38

13. A “composite identifier” is defined as a composite attribute that is an identifier.Answer: False Level: hardPage: 38

14. An identifier may be either unique or non-unique.Answer: True Level: moderatePage: 38

15. E-R modeling recognizes both relationship classes and relationship instances.Answer: True Level: easyPage: 38

16. Relationships do not have attributes.Answer: False Level: moderatePage: 38

17. A single relationship class involves only one entity class.Answer: False Level: hardPage: 38

18. A binary relationship is a relationship based on numerical entity instance identifiers.Answer: False Level: moderatePage: 38

19. The degree of a relationship is expressed as the relationship’s maximum cardinality.Answer: False Level: hardPage: 39

20. A relationship’s minimum cardinality indicates whether or not an entity must be involvedin the relationship.Answer: True Level: easyPage: 39

21. Relationships among instances of a single entity class are called redundant relationships.Answer: False Level: moderatePage: 40

22. 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 Level: hard

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Page: 41 23. ID-dependent entities are a common type of weak entity.

Answer: True Level: moderatePage: 41

24. All weak entities must have a minimum cardinality of 1 on the entity on which it depends.Answer: True Level: hardPage: 42

25. Multi-value attributes are represented in E-R diagrams by creating a new weak entity to represent the multi-value attribute and creating a 1:N relationship.Answer: True Level: moderatePage: 42

26. Subtype entities are used to produce a closer-fitting model when an entity has setsof optional attributes.Answer: True Level: easyPage: 44

27. Entities with an IS-A relationship should have the same identifier.Answer: True Level: easyPage: 44

28. Inheritance in a generalization hierarchy means that the supertype entity inherits all the attributes of the subtype entity.Answer: False Level: moderatePage: 45

29. Where the extended E-R model uses the term “entity,” the IDEF1X model uses theterm generic entity.Answer: False Level: easyPage: 46

30. Where the extended E-R model uses the term “supertype entity,” the IDEF1X model uses theterm generic entity.Answer: True Level: easyPage: 46

31. Where the extended E-R model uses the term “1:N relationship,” the IDEF1X model uses theterm identifying connection relationshipAnswer: False Level: moderatePage: 46

32. Where the extended E-R model uses the term “N:M relationship,” the IDEF1X model uses theterm non-specific relationshipAnswer: True Level: moderatePage: 46

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33. There is no term in the extended E-R model for the IDEF1X model term domain.Answer: True Level: moderatePage: 46

34. In IDEF1X modeling, connection relationships are always drawn from a child entity toa parent entity.Answer: False Level: moderatePage: 49

35. In IDEF1X modeling, the default non-identifying connection relationship is a 1:1 relationship.Answer: False Level: moderatePage: 49

36. In IDEF1X modeling, the default non-identifying connection relationship is a mandatory parent entity connected to an optional child entity.Answer: True Level: moderatePage: 49

37. In IDEF1X modeling, an identifying connection relationship implies that the primary key of the parent entity is part of the primary key of the child entity.Answer: True Level: moderatePage: 49

38. In IDEF1X modeling, there is no way to document a weak entity that is not anID-dependent entity.Answer: True Level: hardPage: 49

39. In IDEF1X modeling, a non-specific relationship is a 1:N or N:1 relationship.Answer: False Level: hardPage: 50

40. When an IDEF1X model is implemented as a relational database, a non-specific relationshipwill be converted into two 1:N relationships.Answer: True Level: moderatePage: 50

41. In IDEF1X modeling, a domain is a named set of possible values for an attribute.Answer: True Level: easyPage: 55

42. UML is intended for modeling and designing object-oriented programs and applications.Answer: True Level: easyPage: 57

43. For database design, UML-style E-R diagrams must be treated very differently from traditionalE-R diagrams because of their object-oriented background.Answer: True Level: moderate

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George Kent Guarino, 01/03/-1,

Where is this?


Page: 5744. Maximum cardinalities are represented in UML-style E-R diagrams with the same

notation (1:1, 1:N, N:M) as in traditional E-R diagrams.Answer: False Level: moderatePage: 58

45. In UML-style E-R diagrams, a weak entity is shown by placing a filled-in diamond on the line to theparent of the weak entity.Answer: True Level: moderatePage: 58

46. One weakness of UML-style E-R diagrams is that there is no means of distinguishingbetween a weak entity that is ID-dependent and a weak entity that is not ID-dependent.Answer: False Level: hardPage: 58

47. UML-style E-R diagrams allow for the existence of class attributes, which are attributes thatpertain to the collection of all entities within that class not to the individual entity instancesthemselves.Answer: True Level: hardPage: 60

48. UML-style E-R diagrams allow for the visibility of attributes.Answer: True Level: easyPage: 60

49. UML-style E-R diagrams introduce object-oriented notation that is of limited practical valuein traditional, relational database design.Answer: True Level: easyPage: 61

Multiple Choice Questions

50. Which of the following is not one of the three schemas used in the ANSI/SPARCthree schema model?a.) externalb.) internalc.) implementationald.) conceptuale.) All of the above are names of the schemas used in the model.

Level: easyPage: 32

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Where is this?


51. Which of the three schemas used in the ANSI/SPARC three schema model is a representation of how users view the database?a.) externalb.) internalc.) implementationald.) conceptuale.) All of the schemas are consistent with this description.

Level: easyPage: 32

52. Which of the three schemas used in the ANSI/SPARC three schema model is a complete logical view of the database?a.) externalb.) internalc.) implementationald.) conceptuale.) All of the schemas are consistent with this description.

Level: easyPage: 32

53. Which of the three schemas used in the ANSI/SPARC three schema model shows physical storage using a particular product or technique?a.) externalb.) internalc.) implementationald.) conceptuale.) All of the schemas are consistent with this description.

Level: easyPage: 32

54. When discussing a data model under construction, users will speak in termsof the ____________ schema that they work with, which database developers musttranslate into a ___________ schema.a.) external, internalb.) external, conceptualc.) internal, implementationald.) internal, conceptuale.) conceptual, implementational

Level: moderatePage: 32

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55. Which of the following is not a key element of E-R models?a.) identifiersb.) entitiesc.) objects d.) attributese.) relationships


56. The representation of a particular entity is called a(n) ______________.a.) entity classb.) entity relationshipc.) entity instance d.) entity attributee.) None of the above.

Level: easyPage: 37

57. Attributes may be ____________ attributes.a.) compositeb.) elementc.) multi-valued.) both a and c e.) both b and c


58. An identifier may be .a.) compositeb.) uniquec.) a single attributed.) non-uniquee.) All of the above.


59. Which type of identifier is used to identify a set of instances of a given entity?a.) classb.) attributec.) uniqued.) instancee.) non-unique

Level: moderate

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Page: 38 60. A composite attribute is an attribute that .

a.) is multi-valueb.) describes a characteristic of the relationshipc.) consists of a group of attributes d.) is calculated at run-timee.) is an identifier

Level: easyPage: 38

61. 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 be.) Both a and c

Level: hardPage: 38

62. 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 classb.) the minimum number of entity classes involved in a relationshipc.) whether or not an instance of one entity class is required to be related to an instance

of another entity classd.) whether or not an entity is a weak entitye.) None of the above.


63. A hash mark across the relationship line near an entity indicates .a.) a maximum cardinality of “one”b.) a unique identifierc.) a minimum cardinality of “zero”d.) a maximum cardinality of “many”e.) None of the above.


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64. To represent a multi-value attribute in an E-R model, ______________________.a.) create a new weak entity with a 1:N relationship

b.) create a new subtype entity with a 1:1 relationshipc.) create a new strong entity with a 1:1 relationshipd.) create a new weak entity with a 1:1 relationshipe.) create a new subtype entity with a 1:N relationship

Level: hardPage: 42

65. Supertype / subtype entities are said to have a(n) __________________ relationship.a.) HAS-Ab.) IS-A c.) recursived.) redundante.) multi-value

Level: easyPage: 43

66. 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.

Level: moderatePage: 43-45

67. 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 a maximum of 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.) 0:1b.) 1:1c.) 1:Nd.) N:1 e.) N:M

Level: hardPage: 38

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ORDER CUSTOMER


68. In terms of generalization hierarchies, the characteristic of “inheritance” means that:

a.) the attributes of an instance of the supertype include the attributes of the subtype.b.) an instance of the supertype must belong to one of the subtypes.c.) the attributes of an instance of the subtype include the attributes of the supertype.d.) there is a redundant relationship among instances of the subtype.e.) the attributes of different subtypes must not overlap with each other.

Level: hardPage: 45

69. Where the extended E-R model uses the term “entity,” the IDEF1X model uses theterm ______________.a.) entityb.) supertype entityc.) subtype entityd.) generic entitye.) category entity

Level: easyPage: 46

70. Where the extended E-R model uses the term “subtype entity,” the IDEF1X model uses theterm ______________.a.) entityb.) supertype entityc.) subtype entityd.) generic entitye.) category entity

Level: easyPage: 46

71. Where the extended E-R model uses the term “1:N relationship,” the IDEF1X model uses theterm ______________.a.) relationshipb.) non-identifying connection relationshipc.) identifying connection relationshipd.) non-specific relationshipe.) domain


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72. Where the extended E-R model uses the term “N:M relationship,” the IDEF1X model uses theterm ______________.a.) relationshipb.) non-identifying connection relationshipc.) identifying connection relationshipd.) non-specific relationshipe.) domain


73. There is no term in the extended E-R model for the IDEF1X model term ______________.a.) relationshipb.) non-identifying connection relationshipc.) identifying connection relationshipd.) non-specific relationshipe.) domain


74. IDEF1X models can be drawn showing: a.) entities only.b.) entities and primary keys.c.) entities, primary keys and attributes.d.) a and be.) a, b, and c

Level: easyPage: 47

75. Drawings of IDEF1X models cannot show: a.) entities.b.) identifying connection relationships.c.) non-identifying connection relationships.d.) domains.e.) primary keys.

Level: moderatePage: + IDEF1X

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Where is this?


76. IDEF1X modeling tools can be used for: a.) external schema modeling.b.) internal schema modeling.c.) conceptual schema modeling.d.) a and be.) b and c

Level: hardPage: + IDEF1X

77. In IDEF1X modeling, a non-identifying connection relationship is indicated by: a.) a solid single connecting line.b.) a dashed single connecting line.c.) a solid double connecting line.d.) a dashed double connecting line.e.) a solid single line combined with a dashed single line.

.Level: moderatePage: 49

78. In IDEF1X modeling, the default non-identifying connection relationships implies that: a.) the relationship is 1:1, with a mandatory parent entity and an optional child entity.b.) the relationship is 1:1, with a optional parent entity and a mandatory child entity.c.) the relationship is 1:N, with a mandatory parent entity and an optional child entity.d.) the relationship is 1:N, with a optional parent entity and a mandatory child entity.e.) the relationship is 1:N, with a mandatory parent entity and a mandatory child entity.


79. In IDEF1X modeling, if a Z is placed at one end of a relationship, it implies that: a.) the relationship is 1:1, with exactly one child entity required.b.) the relationship is 1:1, with either zero or one child entities required.c.) the relationship is 1:N, with exactly one child entity required.d.) the relationship is 1:N, with either zero or one child entities required.e.) the relationship is a categorization relationship, with exactly one category entity required.


80. In IDEF1X modeling, an identifying connection relationship implies that: a.) the primary key of the parent entity is part of the primary key of the child entity.b.) the primary key of the child entity is part of the primary key of the parent entity.c.) the relationship is 1:N, with exactly one child entity required.d.) the relationship is 1:N, with either zero or one child entities required.e.) the relationship is a categorization relationship, with exactly one category entity required.


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Where is this?


81. In IDEF1X modeling, a non-identifying weak entity is annotated with: a.) the letter N next to the weak entity.b.) the letter P next to the weak entity.c.) the letter W next to the weak entity.d.) the letter Z next to the weak entity.e.) nothing.

Level: hardPage: 49

82. In IDEF1X modeling, a non-specific relationship means that the relationship is: a.) 0:1b.) 1:1c.) 1:Nd.) N:1e.) M:N

Level: easyPage: 50

83. When an IDEF1X model is implemented as a relational database, a non-specific relationshipwill be converted into: a.) one 1:1 relationshipb.) one 1:N relationshipc.) two 1:N relationshipsd.) one M:N relationshipe.) two M:N relationships


84. In IDEF1X modeling, E-R model subtypes are called ________________ and may be combined into _______________.a.) generic entities; generic groupsb.) generic entities; generic clustersc.) category entities; category groupsd.) category entities; categorizatione.) discriminator entities; discriminants

Level: easyPage: 52

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85. In IDEF1X modeling, a discriminator is: a.) an attribute of the generic entity that indicates which category entity class

is associated with a generic entity instance.b.) an attribute of the category entity that indicates its associated generic entity class.c.) a symbol used with identifying connection relationships used

as categorization relationships.d.) a symbol used with non-identifying connection relationships used

as categorization relationships.e.) a symbol used with non-specific connection relationships used

as categorization relationships.


86. In IDEF1X modeling, a domain is: a.) an attribute of the generic entity that indicates which category entity

class is associated with a generic entity instance.b.) an attribute of the category entity that indicates its associated generic entity class.c.) a named set of possible values for an attributed.) a named set of possible attributes for an entitye.) a named set of possible category entities in a categorization relationship.

Level: easyPage: 55

87. Which of the following is true about UML?a.) UML is a methodology for developing OOP systems.b.) UML is a set of tools to support the development OOP systems.c.) UML is primarily focused on database development.d.) Both a and b are correct. e.) All of the above are correct.

Level: hardPage: 57

88. In UML-style E-R diagrams, the second segment of an entity class contains _______________.a.) the name of the entityb.) the cardinalities of the entityc.) constraints and methodsd.) relationshipse.) entity attributes

Level: easyPage: 57

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89. Which of the following would indicate a minimum cardinality of 1 and a maximum cardinality of many in UML notation?a.) 1:Nb.) 1 .. Nc.) 1 / *d.) 1 .. * e.) 1: *


90. In UML-style E-R diagrams, the third segment of an entity class contains ________________.a.) the name of the entityb.) the cardinalities of the entityc.) constraints and methods d.) relationshipse.) entity attributes

Level: easyPage: 57

91. Which of the following is not a true statement about the current version of UML?a.) UML places a filled-in diamond on the parent of a weak entity.b.) UML does not provide a means to document exclusivity among subtypes.c.) UML uses the label <identifying> to document an ID-dependent relationship.d.) UML does not provide a means of identifying a recursive relationship. e.) UML shows the cardinality on the parent entity of a weak entity as simple “1.”

Level: hardPage: 58

92. In UML-style E-R diagrams, which of the following would be considered a class attribute of the entity class CUSTOMER?a.) Customer Name (meaning, the first and last name of the customer)b.) Customer Address (meaning, the street, city, state, and zip code of the customer’s

residence)c.) Customer Count (meaning, the count of the number of customers)

d.) Customer Number (meaning, an assigned number to uniquely identify a customer)e.) Both a and b

Level: hardPage: 60

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93. Which of the following is not a characteristic that was introduced to E-R diagramming by UML?a.) class attributesb.) relationship attributes c.) visibility of attributesd.) methodse.) constraints

Level: hardPage: 59-60

94. In UML, an attribute preceded by a ________ is “protected.”a.) !b.) # c.) -d.) +e.) <Persistent>


95. In UML, an attribute that is accessible only by methods of its entity class or of itssubclasses is said to be ____________.a.) privateb.) exclusivec.) protected d.) publice.) persistent

Level: easyPage: 60

96. In UML, an attribute that is accessible only by methods of its entity class issaid to be __________.a.) private b.) exclusivec.) protectedd.) publice.) persistent

Level: easyPage: 60

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Where is this?


97. In UML, an attribute that is accessible and can be changed by any method of anyobject is said to be ______________.a.) privateb.) exclusivec.) protectedd.) publice.) persistent

Level: easyPage: 60

98. In the UML-style entity class ORDERS shown above, “SumOfOrders” is _______________.a.) an entity attributeb.) a methodc.) a constraintd.) a class attribute e.) None of the above.

Level: easyPage: 60

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ORDERS

-SumOfOrders

-OrderNumber-OrderDate-OrderTakenBy

PK Constraint:OrderNumber+GetOrderNo( )+SetOrderDate( )

ORDERS

-SumOfOrders

-OrderNumber-OrderDate-OrderTakenBy

PK Constraint:OrderNumber+GetOrderNo( )+SetOrderDate( )


99. In the UML-style entity class ORDERS shown above, “GetOrderNo( )” is a(n) ___________.a.) private methodb.) protected constraintc.) public constraintd.) public method e.) protected method


Fill in the Blank Questions

100. A(n) schema is a representation of something.Level: easyPage: 32

101. The ANSI/SPARC external schema model is a representation of how usersview the database.

Level: easyPage: 32

102. The ANSI/SPARC conceptual schema model is a complete logical view of the database.Level: easyPage: 32

103. The ANSI/SPARC internal schema model shows physical storage using a particularproduct or technique.

Level: easyPage: 32

104. When designing a data model the users’ views must be translated into thedevelopers’ conceptual schema.


105. A(n) entity is something that the users want to track in their environment. Level: easyPage: 37

106. Entities of a given type are grouped into entity classes . Level: easyPage: 37

107. A(n) instance is the representation of a particular entity. Level: easyPage: 37

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108. A(n) composite attribute consists of a group of attributes. Level: easyPage: 37

109. If an identifier is a(n) unique identifier, it will have one, and only one, entity instance. Level: easyPage: 38

110. Entities can be associated with one another in relationships . Level: easyPage: 38

111. The number of entity classes in a relationship is the degree of the relationship. Level: moderatePage: 38

112. Relationships of degree 2 are referred to as binary relationships. Level: moderatePage: 38

113. To show a minimum cardinality of “one,” a(n) hash mark is placed across the relationship line.


114. To show a minimum cardinality of “zero,” a(n) oval is placed across the relationship line.Level: moderatePage: 39

115. Relationships among entities of a single class are sometimes called recursive relationships.Level: moderatePage: 40

116. In some versions of E-R diagrams, attributes are shown in ellipses attached to the entity to which they belong.

Level: hardPage: 40

117. An entity that is not weak is called a(n) strong entity. Level: easyPage: 41

118. A special type of weak entity in which the identifier of the entity includes the identifier of another entity is called a(n) ID-dependent entity.


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119. Entities containing optional sets of attributes are often represented using subtypes . Level: moderatePage: 43

120. In a generalization hierarchy, the supertype entity contains the attributes that are common to all subtypes.


121. Generalization hierarchies have a characteristic called inheritance , which means that entities in the subtypes have all the attributes of the supertype.

Level: hardPage: 45

122. The IDEF1X model uses the term entity where the extended E-R model usesthe term “entity.”

Level: easyPage: 46

123. The IDEF1X model uses the term category entity where the extended E-R model usesthe term “subtype entity.”

Level: easyPage: 46

124. The IDEF1X model uses the term non-identifying connection relationship where the extended E-R model uses the term “1:N relationship.”


125. The IDEF1X model uses the term non-specific relationship where the extended E-R model uses the term “M:N relationship.”


126. There is no term in the extended E-R model for the IDEF1X model term domain_.Level: moderatePage: 46

127. In IDEF1X modeling, a non-identifying connection relationship is indicated by a dashed line . Level: moderatePage: 49

128. In IDEF1X modeling, the default non-identifying connection relationships implies thatthe relationship is 1:N_.


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Where is this?


Where is this?


129. In IDEF1X modeling, if a Z is placed at one end a relationship, it implies thatthe relationship is 1:1, with either zero or one child entities required.


130. In IDEF1X modeling, a non-specific relationship means that the relationship is M:N . Level: easyPage: 50

131. When an IDEF1X model is implemented as a relational database, a non-specific relationshipwill be converted into two 1:N relationships .


132. In IDEF1X modeling, E-R model subtypes are called category entities .Level: easyPage: 52 Categorization

133. In IDEF1X modeling, a discriminator is an attribute of the generic entity that indicates which category entity class is associated with a generic entity instance.

Level: moderatePage: 52 Categorization

134. In IDEF1X modeling, a domain is a named set of possible values for an attribute. Level: easyPage: 55

135. UML is a set of structures and techniques for designing object-oriented programs and applications.

Level: easyPage: 57

136. In UML-style E-R diagrams, a(n) asterisk means a maximum cardinality of “many.” Level: moderatePage: 58

137. In UML-style E-R diagrams, a filled-in diamond is placed on the line to the parent of a weak entity.


138. When modeling a weak entity in UML-style E-R diagrams, the cardinality on the parent entity is always shown as 1 .

Level: hardPage: 58

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139. In UML-style E-R diagrams, the fact that a weak entity is not ID-dependent is indicated by putting the label <non-identifying> on the relationship.

Level: hardPage: 58

140. In UML-style E-R diagrams, the classes of all entities that are to be stored in the database are labeled with the keyword <Persistent> .

Level: hardPage: 59

141. In UML-style E-R diagrams, an attribute that is preceded by a “+” has a visibility of public . Level: hardPage: 60

142. In UML-style E-R diagrams, an attribute that is preceded by a “#” has a visibility of protected .Level: hardPage: 60

143. In UML-style E-R diagrams, an attribute that is preceded by a “-“ has a visibility of private . Level: hardPage: 60

Essay Questions

144. Describe and discuss schemas and the ANSI/SPARC three schema model.

A schema is a representation of some real-world system of interest to the person creating the schema. Created by the American National Standards Institute/Standards Planning and Requirements Committee (ANSI/SPARC), the ANSI/SPARC three schema model is used in data modeling and database development. The external schema, also known as the user view, illustrates how users see the database. The conceptual schema is the complete logical view of the database developed by the database developer. The internal schema shows how the conceptual schema will be physically implemented by a specific product or technique. The job of the database developer is to translate the users’ external schemas into the conceptual schema. The specific DBMS product used to implement the database will generally translate the conceptual schema into an internal schema.

145. Explain the ambiguity in the definition of a weak entity.

The traditional definition of a weak entity is an entity that cannot exist in the database unless another entity exists in the database. Taken literally, this would include any entity that has a minimum cardinality of “1” to another entity since it could not be placed into the database without the existence of the second entity. Many people feel that this definition is too broad. Therefore, an alternative definition of a weak entity that would require an entity to logically depend on another entity in order to be considered weak has been presented. Under this more narrow definition, all entities that have a minimum cardinality of “1” to another entity would not be considered weak.

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146. Explain the concept of a generalization hierarchy and how it is represented in a traditional E-R diagram.

A generalization hierarchy is 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. 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. However, generalization hierarchies have a characteristic called “inheritance,” which indicates that all subtypes include, or inherit, all the attributes of the supertype. 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.

147. Describe the relationships used in the IDEF1X standard and how they correspond to the relationships found in the extended E-R model.

As used in the extended E-R model, the term "relationship" meant an association between entities, and it still has that basic meaning in the IDEF1X model. All other terms, however, have changed. "HAS-A relationships" in the extended E-R model are called "connection relationships" in the IDEF1X model. There are two types of connection relationships: "non-identifying connection relationships" and "identifying connection relationships." "Non-identifying connection relationships" correspond to" 1:1 relationships" and "1:N relationships" in the extended E-R mode, while "identifying connection relationships" correspond to the extended E-R model's "ID-dependent relationships.” The IDEF1X model "non-specific relationship" is the same as the "M:N relationship" in the extended E-R model. Finally, extended E-R model "IS-A relationships” are called "categorization relationships” in the IDEF1X model.

148. What new contributions to data modeling do UML-style E-R diagrams introduce? How valuableare these from a practical perspective?

UML-style diagrams are a relatively new technique that focus on object-oriented application design. UML-style diagrams introduce new, object-oriented, concepts to data modeling, such as persistence, class attributes, visibility of attributes, and methods. All of these concepts are of limited practical value to actual database design since they cannot be easily or effectively represented in a relational database.

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chapter 02 review

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