Exam 1-Chapter 4

Question 1

The Entity Relationship Model (ERM)

Answer 1

• ERD represents conceptual database as viewed by end user

- ERDs depict database’s main components: entities, attributes, relationship

Question 2

Entities

Answer 2

Refers to eneity set and not to a single entity occurrence; corresponds to table and not to row in relational environment; in Chen and Crow’s Foot models, entity is represented by rectangle with entity’s name; entity name, a noun, written in capital letters

Question 3

Attirbutes

Answer 3

Characteristics of entities; Chen notation; attributes represented by ovals connected to entity rectangle with a line (each oval contains the name of attribute it represents; Crow’s Foot notation: attributes written in attribute box below entity rectangle

Question 4

Required Attribute

Answer 4

Must have a value’ boldfaced in Crow’s Foot notation

Question 5

Optional Attribute

Answer 5

May be left empty

Question 6

Domain

Answer 6

Set of possible values for an attribute; attributes may share a domain

Question 7

Identifiers (Primary Keys)

Answer 7

One or more attributes that uniquely identify each entity instance; boldfaced and underlined in the table structure

Question 8

Compostie Identifer

Answer 8

Primary key composed fo more than one attribute

Question 9

Composite Attribute

Answer 9

Can be subdivided

Question 10

Simple Attribute

Answer 10

Cannot be subdivided

Question 11

Single-Value Attribute

Answer 11

Can have only a single value

Question 12

Multivalued Attributes

Answer 12

Can have many values (double lines in the Chen ERM; Not identified in Crow’s Foot)
M:N relationships and multivaled attributes should not be implemented in the RDBMS

Question 13

Derived (Computed) Attribute

Answer 13

Vale may be calculated from otehr attributes; need not be physically stored within database

Question 14

Relationships

Answer 14

Association between entities; Participants are entities that participate in a relationship; relationship name is a verb; relationships between entities always operate in both directions

Question 15

Connectivity

Answer 15

Describes the relationship classification (type)

Question 16

Cardinality

Answer 16

Expresses minimum and maximum number of entity occurrences associated with one occurrence of related entity

Question 17

Existence Dependence

Answer 17

entity exists in database only when it is associated with another related entity occurrence
It has a mandatory foreign key attribute that cannot be null

Question 18

Existence Idependence

Answer 18

Entity can exist apart from one or more related entities

Sometimes such an entity is referred to as a strong or regular entity

Question 19

Weak (Non-Identifying) Relationship

Answer 19

Exists if the PK of the related entity does not contain a PK component of the parent entity (i.e., the foreign key is not part of the primary key)
Dashed line in Crow’s Foot

Question 20

Strong (Identifying) Relationship

Answer 20

Exists when the PK of the related entity contains a PK component of the parent entity
Solid line in Crow’s Foot

Question 21

Weak Entities

Answer 21

Meet two conditions (is existence-dependent=it cannot exist without the entity with which it has a relationship; its primary key is partially or totally derived from parent entity in relationship)
A strong relationship indicates that the related entity is weak
Database designer determines whether an entity is weak based on business rules

Question 22

Optional Participation (in a relationship)

Answer 22

One entity occurence does not require a corresponding entity occurrence in a particular relationship

Question 23

Mandatory Participation

Answer 23

One entity occurrence requires corresponding entity occurrence in particular relationship

Question 24

Unary Relationship

Answer 24

Association is maintained within single entity

Question 25

Binary Relationship

Answer 25

Two entities are associated

Question 26

Ternary Relationship

Answer 26

Three entities are associated

Question 27

Associative (Composite) Entities

Answer 27

Also known as bridge entities

• Used to implement M:N relationships
• Composed of primary keys of each of the entities to be connected
• May also contain additional attributes that play no role in connective process