Entity Relationship Modeling (Week 2)

Question 1

Entities

Answer 1

Object of interest to the end user

Question 2

Entity Instance / Occurence

Answer 2

A table row in ERM

Question 3

Attributes

Answer 3

Characteristics of Entities (columns in table)

Question 4

Required Attribute

Answer 4

Attributes that must have a value

Question 5

Optional Attribute

Answer 5

Attribute that does not require a value

Question 6

Domain

Answer 6

A set of possible values for a given attribute

Question 7

Identifiers

Answer 7

One or more attributes that uniquely identify each entity instance (Primary Key)

Question 8

Composite Identifier

Answer 8

A primary key composed of more than one attribute

Question 9

Derived/Computed Attribute

Answer 9

Attribute whose value is calculated (derived) from other attributes via an algorithm (not physically stored within the database)

Question 10

Participants

Answer 10

Entities that participate in a relationship

Question 11

Cardinality

Answer 11

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

Question 12

Existence - Dependent

Answer 12

A property of an entity whose existence depends on one or more other entities

Question 13

Existence - Independent

Answer 13

A property of an entity that can exist apart from one or more related entities

Question 14

Strong entity

Answer 14

An entity that is existence-independent, can exist apart from all of its related entities

Question 15

Weak (Non-Identifying) Relationships

Answer 15

A relationship in which the primary key of the related entity does not contain a primary key component of the parent entity

Question 16

Strong (Identifying) Relationship

Answer 16

Exist when the primary key of the related entities contain a primary key component of the parent entity

Question 17

Weak Entity

Answer 17

An entity that displays existence dependence and inherits the primary key of its parent entity

Question 18

Relationship Degree

Answer 18

Number of entities or participants associated with a relationship. Can be unary, binary, temary or higher

Question 19

Unary Relationship

Answer 19

Describe an association within an entity i.e. Employee might manage another employee

Question 20

Binary Relationship

Answer 20

Relationship between two entities

Question 21

Ternary Relationship

Answer 21

Relationship between three entities i.e. Doctor, Drug & Patient

Question 22

Recursive Relationship

Answer 22

A relationship can exist between occurrences of the same entity set

Question 23

Single-Valued Attributes

Answer 23

An attribute with a single value i.e. serial number

Cannot be subdivided into meaningful components

Question 24

Multivalued Attributes

Answer 24

Have many values

An attribute that can have many values for a single entity occurrence

I.e. Degree, can have various strings i.e. BBA, MBA, PHD

Question 25

Composite Attribute

Answer 25

An attribute that can be further subdivided to yield additional attributes i.e. phone number can divide into area code