chapter 4

Question 1

what is cardinality

Answer 1

A property of an end of a relationship between X and Y that describes how many of X is related to Y

Question 2

what is a relationship

Answer 2

It is the connection or association between objects

Question 3

what is optionality

Answer 3

A property of an end of a relationship between X and Y that describes whether X must be or may be related to Y

Question 4

when does it make sense to subdivide an entity

Question 4

when does it make sense to subdivide an entity

Answer 4

This may be the case when a group of instances has special properties, such as attributes or relationships that exist only for that group

in this case the entity is called super type and the groups are called subtypes

Question 5

what are the characteristics of subtypes

Answer 5

• -> Inherits all attributes of the supertype
• -> Inherits all relationships of the supertype
• -> Usually has its own attributes or relationships
• -> Is drawn within the supertype
• -> Never exists alone
• -> May have subtypes of its own

Question 6

when an ER model is complete subtypes ____________-

Answer 6

never stand alone

Question 7

a single subtype is exactly the same as _________

Answer 7

supertype

Question 8

what are the 2 subtype rules

Answer 8

–> Exhaustive: Every instance of the supertype is also an instance of the subtype. All subtypes are listed without omission

–> Mutually exclusive: Each instance of a supertype is an instance of only one subtype

Question 9

what is good practice in the conceptual modelling stage

Answer 9

it is good practice to include the OTHER subtype to make sure that your subtypes are exhaustive – that you are handling every instance of the supertype

Question 10

since subtypes always exist when should you use subtypes

Answer 10

when a need exists within the business to show similarities and differences between instances, then subtype

Question 11

what are the 3 questions to see if the subtype is properly identified

Answer 11

− Is this subtype a kind of supertype?
− Have I covered all possible cases? (exhaustive)
− Does each instance fit into one and only one subtype? (mutually exclusive)

Question 12

what is a structural business rule

Answer 12

structural business rule indicates the types of information to be stored (attributes) and how the information elements interrelate(relationships).

Question 13

what are procedural business rules

Answer 13

• -> procedural rules deal with the prerequisties, steps, processes, or workflow requirements of the business
• -> many procedural business rules are related to time: event A must happen before event B

Question 14

what is the difference between structural business rule and procedural business rule

Answer 14

• -> structural business rules can nearly always be diagrammed in the ERD
• -> some procedural business rules cannot be diagrammed, but must still be documented so that they can programmed later.

Question 15

what is an example of a structural business rule

Answer 15

all teachers who teach at a school must possess a teaching license (attribute)

all orders in a restaurants must be handled by a staff member (relationship)

Question 16

what are some examples of procedural rules

Answer 16

a students must pass algebra and geometry to study trigonometry

Question 17

what is an enhanced er model

Answer 17

extends original ER model with new modeling constructs

Question 18

what is the definition of subtype

Answer 18

A subgrouping of the entities in an entity type that has

attributes distinct from those in other subgroupings

Question 19

define a supertype

Answer 19

A generic entity type that has a relationship with one or more subtypes

Question 20

what is attribute inheritance

Answer 20

• subtype entites inherit values of all attributes in the supertype
• an instance of subtype is also an instance of a supertype

Question 21

what is generalisation

Answer 21

The process of defining a more general entity type from a set of more specialized entity types. BOTTOM-UP

Question 22

what is specialisation

Answer 22

The process of defining one or more subtypes of the supertype and forming supertype/subtype relationships.

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