Ch 4-5

Question 1

E-R Model Components

Answer 1

Entities, Attributes, and Relationships

Question 2

Entities

Answer 2

Refers to the entity set, not an entity occurrence

Question 3

Entity instance

Answer 3

A row in a table corresponds to it

Question 4

Rectangle

Answer 4

An entity is represented by it containing the entity’s name

Question 5

Attributes

Answer 5

Represented by ovals and are connected to the entity with a line
Have a domain-the attribute’s set of possible values
May share a domain
Primary keys are underlined

Question 6

Simple attribute

Answer 6

Cannot be subdivided
Ex: Age, Sex, and Martial status

Question 7

Composite Attribute

Answer 7

Can be further subdivided to yield additional attributes

Question 8

Single-valued attribute

Answer 8

Can have only a single value

Question 9

Multivalued attribute

Answer 9

Can have many values

Question 10

Multivalued Attribute in Relational DBMS

Answer 10

Relational DBMS cannot implement multivalued attributes

Question 11

Derived attribute

Answer 11

Not physically stored within the databases; its value is computed from other attributes
Indicated using a dotted line connecting the attribute with the entity

Question 12

Relationship

Answer 12

An association between entities
Describes as verbs
Represented by diamond-shaped symbols

Question 13

Unary Relationship

Answer 13

Exists when an association is maintained within a single entity (Recursive relationship)

Question 14

Binary Relationship

Answer 14

Exists when two entities are associated (Most common)

Question 15

Ternary relationship

Answer 15

Three entities participate

Question 16

Connectivity

Answer 16

Describe the relationship classification

Question 17

Cardinality

Answer 17

Expresses the specific number of entity occurrences associated with one occurrence of the related entity
Determined by an organization’s business policy

Question 18

Existence-Dependent

Answer 18

If an entity’s existence depends on the existence of one or more other entities

Question 19

Dependence

Answer 19

Table can’t exist on its own
Always depend on another entity
Weak Entity

Question 20

Independence

Answer 20

Table can exist on its own
Strong Entity

Question 21

Participation

Answer 21

Is optional if one entity occurrence does not require a corresponding entity occurrence in a particular relationship

Question 22

Optional entity

Answer 22

Shown by small circle on the side of the optional entity

Question 23

Weak Entity

Answer 23

Existence-dependent on another entity
Has a primary key that is partially or totally derived from its strong counterpart
Indicated by a double rectangle

Question 24

Strong (Identifying) Relationship

Answer 24

Exists when the PK of the related entity contains a PK component of the parent entity
Crow’s Foot model uses a solid line to connect the two entities

Question 25

Weak (Non-Identifying) Relationship

Answer 25

Exists when the PK of the related entity does not contain a PK component of the parent entity Crow's Foot model uses a dashed line to connect the two entities

Question 26

Recursive Entity

Answer 26

One in which a relationship can exist between occurrence of the same entity set Found within a unary relationship

Question 27

Composite Entity

Answer 27

Often created in the process of replacing a M:N relationship by a pair of 1:M relationships Serves as a bridge between the relate entities Composed of the primary keys May contain additional attributes

Question 28

Supertype-Subtype (ISA relationship, Generalization-Specialization hierarchy)

Answer 28

Added to the ER model to create the Enhanced ER model

Question 29

Grouping Entities into types

Answer 29

To avoid NULLs Allows unique attributes

Question 30

Subtype Discriminator

Answer 30

Attributes (data field) that determines the subtype (can be boolean or Integer (ID) or String Value (Type/Code)

Question 31

A subtype entity inherits

Answer 31

the attributes and relationships of the supertype entity and has attributes and relationships unique to itself

Question 32

A subtype entity is created when

Answer 32

Has some unique attributes that do not apply to the supertype entity Participates in relationships that do not apply to the supertype entity

Question 33

Supertype-subtype relationship is modeled as

Answer 33

1:1 relationship in the EER model

Question 34

Completeness constraint

Answer 34

Specifies whether each entity supertype instance is required to be a member of at least one of the subtype

Question 35

Total Completeness

Answer 35

That every supertype occurrence must be a member of at least one subtype

Question 36

Partial Completeness

Answer 36

Some of the supertype instances may not be members of any subtype