1. UML Review

2. Overview: modeling with UML
What is modeling?
What is UML?
Use case diagrams
Class diagrams
Sequence diagrams
Activity diagrams
Statechart diagrams

3. What is modeling?
Modeling consists of building an abstraction of reality.
Abstractions are simplifications because:
They ignore irrelevant details and
They only represent the relevant details.
What is relevant or irrelevant depends on the purpose of the model.

4. Why model software? Software is getting increasingly more complex
Windows XP > 40 mio lines of code
A single programmer cannot manage this amount of code in its entirety.
Code is not easily understandable by developers who did not write it
We need simpler representations for complex systems
Modeling is a mean for dealing with complexity

5. What is UML? UML (Unified Modeling Language)
An emerging standard for modeling object-oriented software.
Resulted from the convergence of notations from three leading object-oriented methods:
OMT (James Rumbaugh)
OOSE (Ivar Jacobson)
Booch (Grady Booch)
Reference: “The Unified Modeling Language User Guide”, Addison Wesley, 1999.
Supported by several CASE tools
Rational ROSE
TogetherJ

6. UML Core Conventions Rectangles are classes or instances
Ovals are functions or use cases
Instances are denoted with an underlined names
myWatch:SimpleWatch
Joe:Firefighter
Types are denoted with non underlined names
SimpleWatch
Firefighter
Diagrams are graphs
Nodes are entities
Arcs are relationships between entities

7. Use Case Diagrams Passenger PurchaseTicket
Used during requirements elicitation to represent external behavior
Actors represent roles, that is, a type of user of the system
Use cases represent a sequence of interaction for a type of functionality
The use case model is the set of all use cases. It is a complete description of the functionality of the system and its environment
Passenger
PurchaseTicket

8. Actors
An actor models an external entity which communicates with the system:
User
External system
Physical environment
An actor has a unique name and an optional description.
Examples:
Passenger: A person in the train
GPS satellite: Provides the system with GPS coordinates
Passenger

9. Use Case
A use case represents a class of functionality provided by the system as an event flow.
A use case consists of:
Unique name
Participating actors
Entry conditions
Flow of events
Exit conditions
Special requirements
PurchaseTicket

10. System Boundary Passenger PurchaseTicket
TicketSystem
Passenger
PurchaseTicket
A system boundary rectangle separates the ticket system from the external actors

11. The <<extends>> Relationship
<<extends>> relationships represent exceptional or seldom invoked cases.
The exceptional event flows are factored out of the main event flow for clarity.
Use cases representing exceptional flows can extend more than one use case.
The direction of a <<extends>> relationship is to the extended use case
Passenger
PurchaseTicket
OutOfOrder
<<extends>>
Cancel
<<extends>>
TimeOut
<<extends>>
NoChange
<<extends>>

12. The <<includes>> Relationship
Passenger
<<includes>> relationship represents behavior that is factored out of the use case.
<<includes>> behavior is factored out for reuse, not because it is an exception.
The direction of a <<includes>> relationship is to the using use case (unlike <<extends>> relationships).
PurchaseMultiCard
PurchaseSingleTicket
<<includes>>
CollectMoney
<<includes>>
NoChange
<<extends>>
Cancel
<<extends>>

13. Use Case Diagrams: Summary
Use case diagrams represent external behavior
An Actor is a role of an object or objects outside of a system that interacts directly with it as part of a coherent work unit (a use case)
<<includes>> and <<extends>> allow common fragments of use cases to be pulled out into a separate use cases
<<includes>> is like a “use case subroutine”
<extends>> is an alternative course of action

14. Class Diagrams
TarifSchedule
Trip
Enumeration getZones()
Price getPrice(Zone)
zone:Zone
Price: Price * *
Class diagrams represent the structure of the system.
Used
during requirements analysis to model problem domain concepts
during system design to model subsystems and interfaces
during object design to model classes.

15. Classes Name Signature Attributes Operations
Table zone2price
Enumeration getZones()
Price getPrice(Zone)
TarifSchedule
Name
zone2price
getZones()
getPrice()
TarifSchedule
Attributes
Signature
Operations
TarifSchedule
A class represent a concept
A class encapsulates state (attributes) and behavior (operations).
Each attribute has a type.
Each operation has a signature.
The class name is the only mandatory information.

16. tarif_1974:TarifSchedule
Instances
tarif_1974:TarifSchedule
zone2price = {
{‘1’, .20}, {‘2’, .40},
{‘3’, .60}}
An instance represents a phenomenon.
The name of an instance is underlined and can contain the class of the instance.
The attributes are represented with their values.

17. Associations * * Associations denote relationships between classes.
TarifSchedule
TripLeg
Enumeration getZones()
Price getPrice(Zone)
Price Zone * *
Associations denote relationships between classes.
The multiplicity of an association end denotes how many objects the source object can legitimately reference.

18. 1-to-1 and 1-to-many Associations
Country
capital
name:String
name:String
One-to-one association
Point *
Polygon
x: Integer
y: Integer
draw()
One-to-many association

19. Many-to-Many Associations
Lists * *
Company
StockExchange
tickerSymbol *
Lists 1
A stock exchange lists many companies each of them uniquely identifed by a ticker symbol used at that stock exchange.
A company can be listed on more than one stock exchange, using the same ticker symbol.
Mercedes Benz is an example for a company listed on more than one stock exchange: Frankfurt and NYSE.
Does it have two different Ticker symbols?
Something not clear here: What happens if the company cannot have the same ticker symbol on two different stock exchanges?
Company
StockExchange
tickerSymbol
SX_ID
qualifier

20. From Problem Statement To Object Model
oblem Statement: A stock exchange lists many companies. Each
company is uniquely identified by a ticker symbol
Class Diagram:
Company
StockExchange * *
Lists
tickerSymbol

21. From Problem Statement to Code: A
stock exchange lists many companies.
Each company is identified by a ticker Symbol
Class Diagram: * *
StockExchange
Company
Lists
tickerSymbol
Java Code
public class StockExchange {
private Vector m_Company = new Vector(); };
public class Company {
public int m_tickerSymbol;
private Vector m_StockExchange = new Vector(); };

22. Aggregation
An aggregation is a special case of association denoting a “consists of” hierarchy.
The aggregate is the parent class, the components are the children class.
A solid diamond denotes composition, a strong form of aggregation where components cannot exist without the aggregate.
Exhaust system
Muffler
diameter
Tailpipe 1
0..2
Exhaust system 1
0..2
Muffler
Tailpipe
diameter
diameter
TicketMachine 3
ZoneButton

23. Inheritance
Button
ZoneButton
CancelButton
The children classes inherit the attributes and operations of the parent class.
Inheritance simplifies the model by eliminating redundancy.

24. Class Relationships
Our class diagram has three kinds of relationships.
association -- a relationship between instances of the two classes. There is an association between two classes if an instance of one class must know about the other in order to perform its work. In a diagram, an association is a link connecting two classes.
aggregation -- an association in which one class belongs to a collection. An aggregation has a diamond end pointing to the part containing the whole. In our diagram, Order has a collection of OrderDetails.
generalization -- an inheritance link indicating one class is a superclass of the other. A generalization has a triangle pointing to the superclass. Payment is a superclass of Cash, Check, and Credit.

25. Composition and aggregation
Associations in which an object is part of a whole are aggregations. Composition is a strong association in which the part can belong to only one whole -- the part cannot exist without the whole. Composition is denoted by a filled diamond at the whole end.
This diagram shows that a BoxOffice belongs to exactly one MovieTheater. Destroy the MovieTheater and the BoxOffice goes away! The collection of Movies is not so closely bound to the MovieTheater.

26. Without qualification
Qualifiers
Directory
File
filename
Without qualification 1 *
With qualification
Directory
File
0…1 1
filename
Qualifiers can be used to reduce the multiplicity of an association.

27. * * An example Account Amount Deposit() Withdraw() GetBalance()
CustomerId
AccountId
Bank
Name
Customer
Name * *
Has
CustomerId
Savings
Account
Withdraw()
Checking
Account
Withdraw()
Mortgage
Account
Withdraw()

28. UML sequence diagrams Used during requirements analysis
selectZone()
pickupChange()
pickUpTicket()
insertCoins()
Passenger
TicketMachine
Used during requirements analysis
To refine use case descriptions
to find additional objects (“participating objects”)
Used during system design
to refine subsystem interfaces
Classes are represented by columns
Messages are represented by arrows
Activations are represented by narrow rectangles
Lifelines are represented by dashed lines

29. Nested messages Dataflow
Passenger
TarifSchedule
Display
ZoneButton
selectZone()
lookupPrice(selection)
price
Dataflow
displayPrice(price)
…to be continued...
The source of an arrow indicates the activation which sent the message
An activation is as long as all nested activations
Horizontal dashed arrows indicate data flow
Vertical dashed lines indicate lifelines

30. …continued from previous slide...
Iteration & condition
Passenger
…continued from previous slide...
CoinIdentifier
Display
CoinDrop
ChangeProcessor *
insertChange(coin)
lookupCoin(coin)
price
Iteration
displayPrice(owedAmount)
Condition
[owedAmount<0] returnChange(-owedAmount)
…to be continued...
Iteration is denoted by a * preceding the message name
Condition is denoted by boolean expression in [ ] before the message name

31. Creation and destruction
Passenger
…continued from previous slide...
ChangeProcessor
Creation
Ticket
createTicket(selection)
print()
Destruction
free()
Creation is denoted by a message arrow pointing to the object.
Destruction is denoted by an X mark at the end of the destruction activation.
In garbage collection environments, destruction can be used to denote the end of the useful life of an object.

32. Sequence Diagram Summary
UML sequence diagram represent behavior in terms of interactions.
Complement the class diagrams (which represent structure).

33. Represent behavior as states and transitions
State Chart Diagrams
State
Initial state
Event
Transition
Final state
Represent behavior as states and transitions

34. Activity Diagrams
An activity diagram shows flow control within a system
An activity diagram is a special case of a state chart diagram in which states are activities (“functions”)

35. Statechart Diagram vs. Activity Diagram
Statechart Diagram for Incident (similar to Mealy Automaton)
(State: Attribute or Collection of Attributes of object of type Incident)
Event causes
State transition
Active
Inactive
Closed
Archived
Incident-
Documented
Incident-
Handled
Incident-
Archived
Activity Diagram for Incident (similar to Moore
(State: Operation or Collection of Operations)
Triggerless
Transition
Completion of activity
causes state transition

36. Activity Diagram: Modeling Decisions

37. Activity Diagrams: Modeling Concurrency
Synchronization of multiple activities
Splitting the flow of control into multiple threads
Splitting
Synchronization

38. Activity Diagrams: Swimlanes
Actions may be grouped into swimlanes to denote the object or subsystem that implements the actions.
Dispatcher
Allocate
Resources
Open
Coordinate
Archive
Incident
Resources
Incident
FieldOfficer
Document
Incident

39. UML Summary
UML provides a wide variety of notations for representing many aspects of software development
Powerful, but complex language
Can be misused to generate unreadable models
Can be misunderstood when using too many exotic features
For now we concentrate on a few notations:
Functional model: Use case diagram
Object model: class diagram
Dynamic model: sequence diagrams, statechart and activity diagrams

40. Problems with UML Semi-formal
Go directly to the class/objects – a low level.
Not good at express temporal information – StateChart