The Entity Relationship Model

Question 1

What does Entity-Relationship (ER) modelling facilitate?

Answer 1

Database design and implementation that accurately reflects the needs of an organisation or system.

Question 2

Define entity type in the context of ER modelling.

Answer 2

A group of objects with the same properties, identified by an enterprise as having an independent existence.

Question 3

What is an entity occurrence?

Answer 3

Each uniquely identifiable object of an entity type.

Question 4

What is the purpose of the ER model?

Answer 4

To support a user’s perception of data and conceal technical aspects of database design.

Question 5

What are the basic concepts of the ER model?

Answer 5

• Entity types
• Relationship types
• Attributes

Question 6

What distinguishes a strong entity type from a weak entity type?

Answer 6

Strong entity types have independent existence; weak entity types are existence-dependent on another entity type.

Question 7

What is a primary key?

Answer 7

A candidate key that is selected to uniquely identify each occurrence of an entity type.

Question 8

What does the term ‘relationship type’ refer to?

Answer 8

A set of meaningful associations among entity types.

Question 9

What is the degree of a relationship?

Answer 9

The number of participating entities involved in a relationship.

Question 10

True or False: A recursive relationship involves the same entity type participating more than once.

Answer 10

True.

Question 11

What is a composite attribute?

Answer 11

An attribute composed of multiple components, each with an independent existence.

Question 12

What does a multi-valued attribute do?

Answer 12

Holds multiple values for each occurrence of an entity type.

Question 13

Fill in the blank: An attribute that represents a value derivable from a related attribute is called a _______.

Answer 13

Derived attribute.

Question 14

What is the notation used to represent a weak entity type?

Answer 14

A double rectangle.

Question 15

What is meant by multiplicity in relationships?

Answer 15

The number (or range) of possible occurrences of an entity type that may relate to a single occurrence of an associated entity type.

Question 16

What does a binary relationship involve?

Answer 16

Two participating entities.

Question 17

How is a ternary relationship defined?

Answer 17

A relationship involving three participating entities.

Question 18

What is a structural constraint?

Answer 18

Constraints that may be placed on entity types participating in a relationship.

Question 19

What is the purpose of an ER diagram?

Answer 19

To visually represent how different pieces of data are related within a system.

Question 20

What does the term ‘candidate key’ refer to?

Answer 20

A minimal set of attributes that uniquely identifies each occurrence of an entity type.

Question 21

What is the significance of role names in relationships?

Answer 21

Role names clarify the purpose of each relationship.

Question 22

What is the maximum degree for relationships typically used in ER models?

Answer 22

Binary (two participating entities).

Question 23

What should an entity be according to ER modelling?

Answer 23

• An object that will have many instances in the database
• An object composed of multiple attributes
• An object we are trying to model

Question 24

What is the notation for associating attributes with relationships?

Answer 24

Dashed line.

Question 25

What is the relationship type called that represents an association between two entities?

Answer 25

Has relationship.

Question 26

What is the multiplicity of a one-to-many relationship?

Answer 26

One entity can relate to many occurrences of another entity.

Question 27

True or False: A weak entity can be identified solely by its own attributes.

Answer 27

False.

Question 28

What does the term 'semantic net' refer to in ER modelling?

Answer 28

A visual representation of relationships among entities.

Question 29

What is an example of a relationship occurrence?

Answer 29

A uniquely identifiable association, which includes one occurrence from each participating entity type.

Question 30

What is the multiplicity of the relationship between Newspaper and PropertyForRent?

Answer 30

Many-to-many (*:*) relationship ## Footnote Each newspaper can advertise one or more properties, and each property can be advertised in zero or more newspapers.

Question 31

What does the notation '1..*' beside the PropertyForRent entity signify?

Answer 31

Each newspaper can advertise one or more properties for rent ## Footnote This indicates mandatory participation of PropertyForRent in the relationship.

Question 32

What does the notation '0..*' beside the Newspaper entity signify?

Answer 32

Each property for rent can be advertised by zero or more newspapers ## Footnote This indicates optional participation of Newspaper in the relationship.

Question 33

What are the two types of restrictions on relationships in multiplicity?

Answer 33

Cardinality and participation ## Footnote Cardinality refers to the maximum number of occurrences, while participation indicates whether all or some entities participate.

Question 34

What is cardinality in the context of ER models?

Answer 34

Maximum number of possible relationship occurrences for an entity in a given relationship type ## Footnote Examples include one-to-one (1..1), one-to-many (1..*), and many-to-many (*..*).

Question 35

What does mandatory participation mean in ER models?

Answer 35

All entity occurrences must participate in a relationship ## Footnote Represented as a minimum value of 1 in multiplicity ranges.

Question 36

What does optional participation mean in ER models?

Answer 36

Only some entity occurrences participate in a relationship ## Footnote Represented as a minimum value of 0 in multiplicity ranges.

Question 37

What is a fan trap in ER modeling?

Answer 37

A situation where a relationship between entity types is ambiguous due to multiple 1:* relationships from the same entity ## Footnote Example: Two 1:* relationships coming from the same Division entity.

Question 38

What is a chasm trap in ER modeling?

Answer 38

A situation where a model suggests a relationship between entity types, but the pathway does not exist for certain occurrences ## Footnote Example: A branch has staff overseeing properties, but not all properties are overseen.

Question 39

What is the minimum multiplicity of the Client entity in the ternary Registers relationship?

Answer 39

0..* ## Footnote Indicates that a Staff entity at a Branch may register zero or more Clients.

Question 40

What is the multiplicity of the Branch entity when Staff/Client values are fixed?

Answer 40

1..1 ## Footnote Indicates that each Branch must have exactly one Staff member in the relationship.

Question 41

What is the UML notation for representing a primary key attribute?

Answer 41

PK_AttributeName ## Footnote Primary key attributes are indicated with {PK} in UML notation.

Question 42

What does 'DerivedAttributeName' represent in UML notation?

Answer 42

An attribute that can be calculated from other attributes ## Footnote Indicated with a forward slash (/) before the attribute name.

Question 43

How is a multi-valued attribute represented in UML notation?

Answer 43

MultiValuedAttributeName {min..max} ## Footnote Indicates the range of possible values for the attribute.

Question 44

What does the notation '1..M' signify in Chen's notation?

Answer 44

One-to-many relationship ## Footnote Indicates that one entity can be associated with multiple occurrences of another entity.

Question 45

What is indicated by a double rectangle in Chen's notation?

Answer 45

Weak entities ## Footnote Strong entities are represented with a single rectangle.

Question 46

What does the Crow's Foot notation represent for a many-to-many relationship?

Answer 46

M:M ## Footnote Indicates that multiple occurrences of one entity can be associated with multiple occurrences of another entity.

Question 47

What should you use for developing ER models in this module?

Answer 47

UML notation ## Footnote Other notations will not be accepted in assessments.