UML Interaction Diagrams

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UML Interaction Diagrams

• April 16 2008

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Quick!

• What is the purpose of interaction diagrams?

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Session Goals

• Understand
• The difference between a class and an object
• Sequence diagrams
• Collaboration diagrams

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Classes vs Objects

• Classes represent abstractions
• Define structure and behavior
• We cannot interact with an abstraction
• An object is an instance of an class
• Run-time entity
• Occupies space in memory
• Can participate in an interaction

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Classes vs. Objects
Java
public class Engine int
numberOfCylindars boolean fuelInjected
public Engine(int cylindarCount,
boolean fuelInjected) public int
getNumberOfCylindars() public boolean
isFuelInjected()
public class Car Engine engine public
Car (int cylindarCount,
boolean fuelInjected) engine new
Engine(cylindarCount,
fuelInjected)
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Classes vs. Objects
Java
createsobject
class
reference
public class Engine int
numberOfCylindars boolean fuelInjected
public Engine(int cylindarCount,
boolean fuelInjected) public int
getNumberOfCylindars() public boolean
isFuelInjected()
public class Car Engine engine public
Car (int cylindarCount,
boolean fuelInjected) engine new
Engine(cylindarCount,
fuelInjected)
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Classes vs. Objects
C
class BilliardBall protected int color
int number Position location public
void setPosition (Position p) void hitBy
(BilliardBall b) void draw()
class Position protected double x
double y double z public void moveTo
(double x, double y,
double z) void transform (Matrix by)
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Classes vs. Objects
C
object
class
class BilliardBall protected int color
int number Position location public
void setPosition (Position p) void hitBy
(BilliardBall b) void draw()
class Position protected double x
double y double z public void moveTo
(double x, double y,
double z) void transform (Matrix by)
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Objects in UML

• Objects
• Have their own notation in UML
• Represented by rectangles (like classes) but
  their label is underlined
• There are multiple ways to denote an object

Class
Object
objectNameClassName
ClassName
ClassName
objectName
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Objects in UML
objectNameClassName
The object is of type Classname and has the name
objectName
objectName
The object has the name objectName but no known
associated type
ClassName
The object is of type Classname but has no known
associated name
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Objects in UML
eightBallBilliardBall
An object called eightball which is an instance
of BillardBall
textWindow
The object has the name textWindow but we do not
know of exactly what type the object is
DiskDrive
The object is of type DiskDrive but we do not
know the name of the object
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Interaction Diagrams

• Class Diagrams
• Show static relationships between classes
• Interaction Diagrams
• Show dynamic interactions between objects
• Basically, what services are used by what classes
  and when

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How do the classes work together?
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Order
Quote
generateQuote() calculateBasePrice()
void calculateDiscounts() void sendQuote()
void
setQuote(quoteInfo String) void
Customer
-modeMgr
getDiscount() double getEmail () String
OrderLine
getDiscount() double getEmail () String
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TimeManager
SixtySecondTimer
TimeManager() setDisplay(newDisplay
Display) void setModeManager(newModeMgr
ModeManager) void setAlarm(newAlarm Alarm)
void
SixtySecondTimer() setTimeManager (newTimeMgr
TimeManager void start() void
-timer
-timeMgr
Clock
ModeManager
-modeMgr
Display
Clock() start() void
ModeManager()
Display()
-buttonMgr
ButtonManager
Alarm
-alarm
ButtonManager() setModeManager(newModeMgr
ModeManager) void setTimeManager(newTimeMgr
TimeManager) void
Alarm()
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Interaction Diagrams

• Since Interaction Diagrams represent run-time
  interactions, they use objects rather than
  classes
• There are two common Interaction Diagrams
• Sequence Diagrams
• Collaboration Diagrams

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Sequence Diagrams vs Collaboration Diagrams

• Both diagrams convey the same information the
  order in which objects call each other under a
  particular set of circumstances
• Sequence Diagrams
• Tend to be more readable with respect to the time
  ordering of events
• Collaboration Diagrams
• Provide a better spatial representation of more
  complicated interactions

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Sequence Diagrams

• Sequence Diagrams are constructed by placing
  objects horizontally across the top of a diagram
• Lifelines extend down from each object
• Various arrow types extend between lifeline to
  indicate messages (i.e., method calls) occurring
  between classes
• The arrow types have different meanings

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Class Diagram - Example
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Sequence Diagrams Example
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Sequence Diagrams Example
objects
lifeline
activation box
messages
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Sequence Diagrams Variation
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Sequence Diagrams Variation
return, denotes return of control
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Class Diagram - Example
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Sequence Diagrams Example
Adapted from Fowler, UML Distilled, p 68
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Sequence Diagrams Example
Adapted from Fowler, UML Distilled, p 68
iterator
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Class Diagram - Example
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Sequence Diagrams Example
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Sequence Diagrams Example
return, denotes return of control
Notice that control is always returned to the
caller!
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Collaboration Diagrams

• Collaboration Diagrams look similar to Class
  Diagrams
• Collaboration Diagrams consist of objects and
  associations between theses objects
• The associations are labeled with a message and a
  direction, indicating one object is calling
  another
• The messages are numbered to show the order in
  which they occur

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Collaboration Diagram Example
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Notes on Interaction Diagrams

• Sequence and Collaboration Diagrams are good
  tools for showing a specific sequence
• They do not lend themselves well to showing
  alternative flows
• It is possible to show alternative flows in
  sequence diagrams but the diagrams can get
  cluttered quickly

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Alternative Flow Example
Branch point with guard conditions
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Asynchronous Messages

• So far we have illustrated synchronous messages
• Synchronous messages prevent the caller from
  continuing until the message is processed by the
  receiver
• This is the usual way in which objects interact
• Asynchronous communication can also be modeled
• Asynchronous messages enable the caller to do
  something else
• Asynchronous messages sometimes requires an
  acknowledgement or answer message

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Asynchronous Messages Class Diagram
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Asynchronous Messages Sequence Diagram
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Asynchronous Messages Example
Asynchronous Messages
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Scenarios and Sequence Diagrams

• Scenarios are often give rise to sequence
  diagrams
• Once system roles are identified, scenarios are
  translated to sequence diagrams that involve
  different system roles
• This provides a visual representation of expected
  system behavior
• The system can be executed, the resulting
  interaction also captured in a sequence diagram
  and the two diagrams compared
• There exist case tools which can help automate
  this process

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Scenarios and Sequence Diagrams - Example

• The following use case is represented by the
  previous sequence diagram