1. Unified Modeling Language
Chapter 4
Squeak: Object-oriented design with multimedia applications

2. Unified Modeling Language
There have been O-O gurus for many years
Three of them worked together to define UML (“Three amigos”: Booch, Rumbaugh, Jacobson)
Has now been approved as a standard by the Object Management Group (OMG)
UML is a notation/language not a process
Diagrams and notation from UML 1.4 definition; 1.5 is the latest; see:

3. Diagrams Class diagrams: Represents static structure
Use case diagrams: Sequence of actions a system performs to yield an observable result to an actor
Sequence diagrams: Shows how groups of objects interact in some behavior
State diagrams: Describes behavior of system by describing states of an object
Plus others

4. UML Class Diagrams Classes are boxes Lines are relationships
Top is name
Middle are attributes
Bottom is services
Lines are relationships
Arrows show navigability

5. How can two classes be related?
Generalization-specialization or IsA
NamedBox IsA Box
Diagram: Triangle on the relationship line
Association or HasA
Box HasA Pen
Diagram: Just a relationship line
Aggregation is a part-whole relationship, but not exclusive
Diagram: Open diamond on the line
Composition is a part-whole relationship that is exclusive
Diagram: Closed diamond on the line
Dependency or TalksTo
Dependency is sort of temporary HasA
Diagram: Dashed line in UML

6. The Aggregation-Association Issue
It’s not clear when, in UML, you notate that one thing “has” another.
Coad: “An example of aggregation is the relationship between an organization and its clerks”
Rumbaugh: “A company is not an aggregation of its employees”
How many OO experts does it take…
Safest: Use an association unless the definition of “aggregation” is clear to your audience

7. More on UML Class Diagrams
Navigability
Both ways or just one? Who knows about the other?
Does the Box have the Pen or the Pen have the Box?
Usually added later in the process
Book is wrong on bidirectional (no arrows is bidirectional, not double arrows.)
Multiplicities
How many Pens per how many Boxes?
Can add labels to indicate how reference is viewed

8. Concrete and Abstract Classes
Concrete classes are those that we create instances from
Abstract classes are never instantiated
They exist to define structure and behavior for other classes to inherit
In UML, abstract classes use italics when naming the class, or <<abstract>> keyword

9. Use Case Diagrams Means of capturing requirements
Document interactions between user(s) and the system
User (actor) is not part of the system itself
But an actor can be another system
An individual use case represents a task to be done with support from the system (thus it is a ‘coherent unit of functionality’)

10. Simple Use Case Diagram
Reserve book
Borrow book
Return book

11. Use Case Diagram with Multiple Actors

12. Use Cases
Are actually defined as text, including descriptions of all of the normal and exception behavior expected
Do not reveal the structure of the system (i.e. the system does…)
Collectively define the boundaries of the system to be implemented
Provide the basis for defining development iterations
Use language of user

13. Use Case Descriptions USE CASE UC1: Process Sale
Primary Actor: Cashier
Stakeholders and Interests:
- Cashier: Wants accurate, fast entry, no payment errors
- Salesperson: Wants commissions updated
- Customer: Wants purchase and fast service. Wants proof
Preconditions: Cashier is identified and authenticated
Postconditions: Sale is saved. Tax correctly calculated. Accounting and inventory are updated. Commissions recorded. Receipt is generated. Payment authorizations are recorded.
Main Success Scenario:
1. Customer arrives at POS checkout with goods/services to buy
2. Cashier starts a new sale.
3. Cashier enters item identifier.
4. System records sale item and presents item description, price, and running total. Price calculated from a set of price rules.

14. Use Case Descriptions Cashier repeats steps 3-4 until indicates done
5. System presents total with taxes calculated. …
Extensions / Exceptions:
*a. At any time, System fails:
To support recovery and correct accounting, ensure all transaction sensitive state and events can be recovered from any step of the scenario.
1. Cashier restarts System, logs in, and requests recovery of prior
State : Restart System.
2. System reconstructs prior state.
3a. Invalid Identifier:
1. System signals error and rejects entry.
Special Requirements:
- Touch screen UI on large flat panel monitor, Text visible from 1 meter
- Credit authorization response within 30 seconds, 90% of time.
Frequency of Occurrence: May be continuous
Open Issues: Explore recovery state, Tax Law variations?

15. Sequence (Event) Diagrams
Shows individual objects and how they interact
Describes
Lifelines of objects
Who sends what messages when
Can also describe sending messages to self ("self-delegation")

16. Example Real Time Sequence Diagram

17. State Diagrams
Describe all the possible states a particular object can get into, and the events that lead to those changes
Also called a "statechart"

18. Example State Diagram

19. UML in Real Practice You don't typically use all the diagrams
You'll choose between them based on preference and particular situation
You typically use many diagrams
A single use case may not capture all scenarios
If you are going to use statecharts, there are probably lots of objects with states
Each sequence diagram only shows one interaction

20. Example: Student Registration System
Not going to do all the diagrams
Not all types, not even all that completely specify the system
But this is an application you know, so the examples may help make sense

21. Student Registration Class Diagram (Early Analysis Level)
Transcript
gradeForCourse:
takenCourse:
Student 1 1
historyRecordedIn *
getsScheduleFrom 1
Registrar
getSectionsFor:
enrollInSection:
dropFromSection:
Section
assigns * * 1
enrollInClass:
daysAndTime
gradeInCourse:
roster
takenCourse: * 1
addStudent
removeStudent * 1 *
majorsIn * * *
CourseGrade
taughtIn
manages 1
Department
requiredCourses 1 *
givenFor
grade
Course
name
number
creditHours
1..3 *
termEnrolled * * * *
prereqs
0..3
owns
hasPrereqs
0..3
0..3
0..3
prereqs

22. Partial Use Case Diagram
Apply for
Admission
Admissions
Enroll in
the University
Student
Enroll in
a Course
Withdraw
from a Course

23. States of a Student Enrolled Registered
Apply [ Must be accepted first ]
Enrolled
EnrollInClass ( Add a Transcript )
Registered
Withdraw
AddCourse
Graduate [ All courses must be completed ]

24. Sequence Diagram: Registering for Course
aStudent:
Student
theRegistrar :
Registrar
aSection :
Section
theTranscript :
Transcript
getSectionsFor:
return sections
enrollInSection:
takenCourse: prerequisite
state of prereq
[havePrereq] addStudent:
enrolled
enrolled

25. UML Tools Most complete tool: Rational Rose, http://www.rational.com
Lots of others
Together by Object International
BOOST (Basic Object-Oriented Support Tool) by Noel Rappin, available on CD/CoWeb
Argo-UML, ObjectPlant, Posiden, etc.
diagramming tools, e.g. Visio, xfig

26. For More Information… Serious O-O designers do use UML
UML Distilled by Martin Fowler is a good practical introduction to UML
Official UML book series published by Addison-Wesley
UML Resource Center