ERD

Question 1

What are a database’s main components?

Answer 1

Entities
Attributes
Relationships

Question 2

Attributes:

Answer 2

Characteristics of entities

Question 3

Required attribute:

Answer 3

Must have a value, cannot be left empty

Question 4

Optional attribute:

Answer 4

Does not require a value, can be left empty

Question 5

Domain:

Answer 5

Set of possible values for a given attribute

Question 6

Identifiers:

Answer 6

One or more attributes that uniquely identify each entity instance

Question 7

Composite identifier:

Answer 7

Primary key composed of more than one attribute

Question 8

Composite attribute:

Answer 8

Attribute that can be subdivided to yield additional attributes

Question 9

Simple attribute:

Answer 9

Attribute that cannot be subdivided

Question 10

Single-valued attribute:

Answer 10

Attribute that has only a single value

Question 11

Multivalued attributes:

Answer 11

Attributes that have many values and require creating:

Several new attributes, one for each component of the original multivalued attribute

A new entity composed of the original multivalued attribute’s components

Question 12

Derived attribute:

Answer 12

Attribute whose value is calculated from other attributes

- Derived using an algorithm

Question 13

Advantages of storing derived attributes:

Answer 13

Saves CPU processing cycles
Saves data access time
Data value is readily available
Can be used to keep track of historical data
Saves storage space
Computation always yields current value

Question 14

Disadvantages of storing derived attributes:

Answer 14

Requires constant maintenance to ensure derived value is current, especially if any values used in the calculation change

Uses CPU processing cycles
Increases data access time
Adds coding complexity to queries

Question 15

Relationships:

Answer 15

Association between entities that always operate in both directions

Question 16

Participants:

Answer 16

Entities that participate in a relationship

Question 17

Connectivity:

Answer 17

Describes the relationship classification

Question 18

Cardinality:

Answer 18

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

Question 19

Existence dependence:

Answer 19

Entity exists in the database only when it is associated with another related entity occurence

Question 20

Existence independence:

Answer 20

Entity exists apart from all of its related entities

Referred to as a strong entity or regular entity

Question 21

Weak (non-identifying) relationship:

Answer 21

Primary key of the related entity does not contain a primary key component of the parent entity

Question 22

Strong (identifying) relationships:

Answer 22

Primary key of the related entity contains a primary key component of the parent entity

Question 23

Weak Entity:

Answer 23

Conditions:

• Existence-dependent
• Has a primary key that is partially or totally derived from parent entity in the relationship

Database designer determines whether an entity is weak based on business rules

Question 24

Optional participation:

Answer 24

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

Question 25

Mandatory participation

Answer 25

One entity occurrence requires a corresponding entity occurrence in a particular relationship

Question 26

Relationship Degree:

Answer 26

Indicates the number of entities or participants associated with a relationship

Question 27

Unary relationship:

Answer 27

Association is maintained within a single entity

Question 28

Recursive relationship:

Answer 28

Relationship exists between occurrences of the same entity set

Question 29

Binary relationship:

Answer 29

Two entities are associated

Question 30

Ternary relationship:

Answer 30

Three entities are associated

Question 31

Associative (Composite) Entities:

Answer 31

• Used to represent an M:N relationship between two or more entities
• Is in a 1:M relationship with the parent entities
• Composed of the primary key attributes of each parent entity
• May also contain additional attributes that play no role in connective process