1. a generalization is a relationship between a general thing (the
Generalization (Ch 26)
a generalization is a relationship between a general thing (the
superclass or parent class) and a more specific kind of thing
(the subclass or child class)
example:
a StaffMember is a specialized kind of LibraryMember
a StudentMember is a specialized kind of LibraryMember
LibraryMember
StaffMember
StudentMember
Sept 2003
Ron McFadyen

2. Multiple subclasses can be grouped to indicate they are related
Generalization (Ch 26)
Multiple subclasses can be grouped to indicate they are related
subclasses
LibraryMember
StaffMember
StudentMember
It then becomes meaningful to consider certain constraints:
complete, incomplete, disjoint, overlapping
Sept 2003
Ron McFadyen

3. Inheritance of attributes and behaviour:
LibraryMember
Generalization
Inheritance of attributes and behaviour:
everything a LibraryMember can do, a StaffMember can do
everything a LibraryMember can do, a StudentMember can do
If a LibraryMember can borrow a book, so can a StaffMember and a StudentMember
a StaffMember and a StaffMember have all the attributes the LibraryMember has, and possibly more
Specialization: there are some things that a specialized class can do that a LibraryMember cannot
StaffMember
StudentMember
Sept 2003
Ron McFadyen

4. a SavingsAccount is a specialized kind of BankAccount
example:
a SavingsAccount is a specialized kind of BankAccount
a ChequingAccount is a specialized kind of BankAccount
a BankAccount is a specialized kind of Asset
RealEstate is …
Asset
RealEstate
BankAccount
Security
SavingsAccount
ChequingAccount
Sept 2003
Ron McFadyen

5. The subclass must conform to 100% of the superclass’s: attributes
Text:
All members of a conceptual subclass set are members of their superclass set
100% of the conceptual superclass’s definition should be applicable to the subclass.
The subclass must conform to 100% of the superclass’s:
attributes
associations
Sept 2003
Ron McFadyen

6. Figure 26.7
Every payment, regardless of whether it is cash, credit, or cheque, has an Amount and it is associated with a Sale
Pays-for
Payment
Sale 1 1
Amount: money
Cash Payment
Credit Payment
Cheque Payment * 1 1 1
CreditCard
Cheque
Sept 2003
Ron McFadyen

7. Motivation for partitioning a conceptual class into subclasses:
subclass has additional attributes of interest
subclass has additional associations of interest
subclass is operated on, handled, reacted to, or manipulated differently than the superclass or other subclasses
the subclass concept represents an animate thing that behaves differently than the superclass or other subclasses
Examples
a chequing account will accrue interest differently from a savings account
a loan account will have different associations from a savings account
Sept 2003
Ron McFadyen

8. The name Payment is italicized - meaning it is an abstract class
Figure 26.12
The name Payment is italicized - meaning it is an abstract class
An abstract class is a class that will never be instantiated; only its subclasses can exist
If “Payment” was not in italics then a Payment could exist that is not a Cash, Credit, or Check payment
Sept 2003
Ron McFadyen

9. Credit Payment and Cheque Payment participate in other associations
Figure 26.7
Credit Payment and Cheque Payment participate in other associations
Pays-for
Payment
Sale 1 1
Amount: money
Cash Payment
Credit Payment
Cheque Payment * 1 1 1
CreditCard
Cheque
Sept 2003
Ron McFadyen

10. ROT: Do not model with subclasses. Model with states.
Watch for objects that are performing roles, or moving from one state to another.
ROT: Do not model with subclasses. Model with states.
Text:
Consider payments that begin as unauthorized and may eventually become authorized.
Do not model as:
Payment
Unauthorized Payment
Authorized Payment
Sept 2003
Ron McFadyen

11. Text: Instead of Figure 26.13 Payment Unauthorized Payment
Use:
Is-in
Payment
PaymentState * 1
Unauthorized State
Authorized State
Sept 2003
Ron McFadyen

12. Every payment has getStatus and cancel operations
Is-in
Payment
PaymentState
Every payment has getStatus and cancel operations * 1
getStatus()
cancel()
A payment that is not authorized has an authorize operation, but authorize cannot be executed by a payment that has already been authorized.
Cancel has two different implementations (polymorphism).
Unauthorized State
Authorized State
authorize()
cancel()
cancel()
Sept 2003
Ron McFadyen

13. Exercise: In some organizations, Purchase Orders and Invoices are modeled as separate classes; in other organizations, they are considered as Orders that evolve over time from being Purchase Order-like to eventually being Invoice-like when they can be paid.
So, in the latter case you have Order and Orderline classes that change state over time. How can we model these?
Sept 2003
Ron McFadyen

14. Shown inside curly braces {…} incomplete complete disjoint overlapping
Constraints
Shown inside curly braces {…}
incomplete
complete
disjoint
overlapping
mammal
{disjoint, incomplete}
dog
cat
Sept 2003
Ron McFadyen

15. Ch 27 - Refining the Domain Model
27.1 Association Classes
27.2 Aggregation and Composition
27.4 Association Role Names
27.5 Roles as Concepts vs Roles in Associations
27.8 Reflexive Associations
27.10 Packages
Sept 2003
Ron McFadyen

16. Aggregation and Composition
both are associations used to denote that an object from one class is part of an object of another class
An example of Aggregation: a course is part of an honours programme. The same module could be part of several honours courses * *
HonoursProgramme
Course
“Software Engineering with Objects and Components” is part of both the “Software Engineering” and the “Computer Science” honours programmes
Sept 2003
Ron McFadyen

17. Aggregation and Composition
Composition is similar to, but stronger than aggregation. If you specify composition, then you are saying that one object owns its parts.
Board
Square *
A Board is made up of several Squares. A Square will belong to just one Board. If a Board is deleted, then its Squares are deleted too.
What is the multiplicity at the composition end of the association?
Sept 2003
Ron McFadyen

18. Aggregation and Composition
Consider Invoices and their Invoice Lines
Question: Is the association aggregation or composition? ? ? *
Invoice
InvoiceLine
Sept 2003
Ron McFadyen

19. Aggregation and Composition
Consider Sales and their SalesLineItems
Is the association an aggregation or a composition? ? ? *
Sale
SalesLineItem
Sept 2003
Ron McFadyen

20. Aggregation and Composition
Consider the Product Catalogue and its Product Specifications.
Is the association an aggregation or a composition?
Consider the General Calendar and its Course Specifications.
Is the association an aggregation or a composition?
Consider the Registration Guide and its Course Offerings.
Is the association an aggregation or a composition?
Sept 2003
Ron McFadyen

21. Aggregation and Composition
Figure 27.6
0..7
Several associations sharing the same aggregation/composition can be drawn with converging lines
Finger
Hand
0..1
Palm
0..1
Thumb
Sept 2003
Ron McFadyen

22. Aggregation and Composition
Suppose a document comprises a TOC, a preface, a number of sections, and possibly an index.
composition or aggregation?
Sept 2003
Ron McFadyen

23. Association Class Figure: 27.3:
Business rule: a store has a different merchant ID for each service
Association Class: a modeling element that is both an association and a class. It has attributes, operations, multiplicities, etc. It can participate in other relationships.
Sept 2003
Ron McFadyen

24. Top of Figure 27.4 (ignore rest of it)
Many to many associations
likely candidate for an Association Class
Limitation !!! each company object can be associated to a person object only once. If we wanted to provide for a person to be employed by the same company more than once, we would need to promote Employment to be a regular class. How do we model this?
Sept 2003
Ron McFadyen

25. Reflexive Association
An association involving the same class more than once. 1
Person 1
marries
Sept 2003
Ron McFadyen

26. Reflexive Association
An association involving the same class more than once. *
Person *
marries
Sept 2003
Ron McFadyen

27. Reflexive Association
An association involving the same class more than once. *
Part *
comprises
Sept 2003
Ron McFadyen

28. Figure 27.11 Contrasting two models
Can be very accurate: one person plays more than one role
More difficult to implement: may need to mutate an object from one class to another
Sept 2003
Ron McFadyen

29. Packages are used to organize model elements.
Figures
27.21 shows the POS Domain package comprising the Payments, Product, etc. packages
27.22 the core package
27.23 the payments package …
name
Sept 2003
Ron McFadyen