ch2lect.ppt

Conquering
Complex
and
Changing
Systems
Object-Oriented
Software
Engineering
Chapter 2,
Modeling with UML

Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 2
Overview
 What is modeling?
 What is UML?
 Use case diagrams
 Class diagrams
 Sequence diagrams
 Activity diagrams
 Summary

Systems, Models, and Views
 A model is an abstraction describing system or a subset of a
system
 A view depicts selected aspects of a model
 A notation is a set of graphical or textual rules for representing
views
 Views and models of a single system may overlap each other

Systems, Models, and Views
Airplane
Flightsimulator
Scale Model
Blueprints
Electrical
Wiring

Models, Views, and Systems (UML)
View
*
*
depicted by
described by
System Model
flightSimulator:Model
scaleModel:Model
blueprints:View
airplane:System
fuelSystem:View electricalWiring:View

Why model software?
Software is already an abstraction: why model software?
 Software is getting larger, not smaller
 NT 5.0 ~ 40 million lines of code
 A single programmer cannot manage this amount of code in its
entirety.
 Code is often not directly understandable by developers who
did not participate in the development
 We need simpler representations for complex systems
 Modeling is a mean for dealing with complexity

Concepts and Phenomena
 Phenomenon: An object in the world of a domain as you
perceive it, for example:
 The lecture you are attending
 My black watch
 Concept: Describes the properties of phenomena that are
common, for example:
 Lectures on software engineering
 Black watches
 A concept is a 3-tuple:
 Its Name distinguishes it from other concepts.
 Its Purpose are the properties that determine if a phenomenon is a
member of a concept.
 Its Members are the phenomena which are part of the concept.

 Abstraction: Classification of phenomena into concepts
 Modeling: Development of abstractions to answer specific
questions about a set of phenomena while ignoring irrelevant
details.
Members
Name
Clock
Purpose
A device that
measures time.
Concepts and Phenomena

Concepts In Software: Type and Instance
 Type:
 An abstraction in the context of programming languages
 Name: int, Purpose: integral number, Members: 0, -1, 1, 2,
-2, . . .
 Instance:
 Member of a specific type
 The type of a variable represents all possible instances the
variable can take.
 The relationship between “type” and “instance” is similar to
that of “concept” and “phenomenon.”
 Abstract data type:
 Special type whose implementation is hidden from the rest of the
system.

Class
 Class:
 An abstraction in the context of object-oriented languages
 Like an abstract data type, a class encapsulates both state
(variables) and behavior (methods)
 Unlike abstract data types, classes can be defined in terms of
other classes using inheritance
Watch
time
date
CalculatorWatch
SetDate(d)
EnterCalcMode()
InputNumber(n)
calculatorState

Object-Oriented Modeling
UML Package
Application Domain Solution Domain
Application Domain Model System Model
Aircraft
TrafficController
FlightPlan Airport
MapDisplay
FlightPlanDatabase
SummaryDisplay
TrafficControl
TrafficControl

Application and Solution Domain
 Application Domain (Requirements Analysis):
 The environment in which the system is operating
 Solution Domain (System Design, Object Design):
 The available technologies to build the system

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
 Together/J
 ...

UML and This Course
 You can model 80% of most problems by using about 20%
UML
 In this course, we teach you those 20%

UML First Pass
 Use case diagrams
 Describe the functional behavior of the system as seen by the user.
 Class diagrams
 Describe the static structure of the system: Objects, Attributes, and
Associations.
 Sequence diagrams
 Describe the dynamic behavior between actors and the system and
between objects of the system.
 Statechart diagrams
 Describe the dynamic behavior of an individual object as a finite state
machine.
 Activity diagrams
 Model the dynamic behavior of a system, in particular the workflow,
i.e. a flowchart.

UML First Pass: Use Case Diagrams
WatchUser WatchRepairPerson
ReadTime
SetTime
ChangeBattery
Actor
Use case
Package
SimpleWatch
Use case diagrams represent the functionality of the system
from user’s point of view

UML First Pass: Class Diagrams
Battery
load()
1
2
Time
now()
PushButton
state
push()
release()
1
1
1
1
1
2
blinkIdx
blinkSeconds()
blinkMinutes()
blinkHours()
stopBlinking()
referesh()
LCDDisplay
SimpleWatch
Class
Association
Multiplicity
Attributes
Operations
Class diagrams represent the structure of the system

UML First Pass: Sequence Diagram
Object
Message
Activation
Sequence diagrams represent the behavior as interactions
blinkHours()
blinkMinutes()
incrementMinutes()
refresh()
commitNewTime()
stopBlinking()
pressButton1()
pressButton2()
pressButtons1And2()
pressButton1()
:WatchUser
:Time
:LCDDisplay
:SimpleWatch

button1&2Pressed
button1&2Pressed
button1Pressed
button2Pressed
button2Pressed
button2Pressed
button1Pressed
button1&2Pressed Increment
Minutes
Increment
Hours
Blink
Hours
Blink
Seconds
Blink
Minutes
Increment
Seconds
Stop
Blinking
UML First Pass: Statechart Diagrams
State
Initial state
Final state
Transition
Event

Other UML Notations
UML provide other notations that we will be introduced in
subsequent lectures, as needed.
 Implementation diagrams
 Component diagrams
 Deployment diagrams
 Introduced in lecture on System Design
 Object Constraint Language (OCL)
 Introduced in lecture on Object Design

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 nonunderlined names
 SimpleWatch
 Firefighter
 Diagrams are graphs
 Nodes are entities
 Arcs are relationships between entities

UML Second Pass: Use Case Diagrams
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

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

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

Use Case Example
Name: Purchase ticket
Participating actor: Passenger
Entry condition:
 Passenger standing in front
of ticket distributor.
 Passenger has sufficient
money to purchase ticket.
Exit condition:
 Passenger has ticket.
Event flow:
1. Passenger selects the number
of zones to be traveled.
2. Distributor displays the
amount due.
3. Passenger inserts money, of
at least the amount due.
4. Distributor returns change.
5. Distributor issues ticket.
Anything missing?
Exceptional cases!

The <<extend>> Relationship
 <<extend>> 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 <<extend>>
relationship is to the extended use
case
Passenger
PurchaseTicket
TimeOut
<<extend>>
NoChange
<<extend>>
OutOfOrder
<<extend>>
Cancel
<<extend>>

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

Class Diagrams
 Class diagrams represent the structure of the system.
 Class diagrams are used
 during requirements analysis to model problem domain concepts
 during system design to model subsystems and interfaces
 during object design to model classes.
Enumeration getZones()
Price getPrice(Zone)
TariffSchedule
* *
Trip
zone:Zone
price:Price

Classes
 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.
zone2price
getZones()
getPrice()
TariffSchedule
Table zone2price
TariffSchedule
Name
Attributes
Operations
Signature
TariffSchedule

Instances
 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.
zone2price = {
{‘1’, .20},
{‘2’, .40},
{‘3’, .60}}
tariff_1974:TarifSchedule

Actor vs. Instances
 What is the difference between an actor and a class and an
instance?
 Actor:
 An entity outside the system to be modeled, interacting with the
system (“Pilot”)
 Class:
 An abstraction modeling an entity in the problem domain, inside the
system to be modeled (“Cockpit”)
 Object:
 A specific instance of a class (“Joe, the inspector”).

Associations
 Associations denote relationships between classes.
 The multiplicity of an association end denotes how many
objects the source object can legitimately reference.
TarifSchedule
*
price
zone
TripLeg
*

1-to-1 and 1-to-Many Associations
1-to-1 association
1-to-many association
*
draw()
Polygon
x:Integer
y:Integer
Point
1
Has-capital
name:String
Country
name:String
City
1
1

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.
1
Exhaust System
Muffler Tailpipe
0..2

Composition
 A solid diamond denote composition, a strong form of
aggregation where components cannot exist without the
aggregate.
3
TicketMachine
ZoneButton

Generalization
 Generalization relationships denote inheritance between
classes.
 The children classes inherit the attributes and operations of the
parent class.
 Generalization simplifies the model by eliminating redundancy.
Button
ZoneButton
CancelButton

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

UML Sequence Diagrams
 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
selectZone()
pickupChange()
pickUpTicket()
insertCoins()
Passenger
TicketMachine

UML Sequence Diagrams: Nested Messages
 The source of an arrow indicates the activation which sent the
message
 An activation is as long as all nested activations
selectZone()
Passenger
ZoneButton TarifSchedule Display
lookupPrice(selection)
displayPrice(price)
price
Dataflow
…to be continued...

Sequence Diagram Observations
 UML sequence diagram represent behavior in terms of
interactions.
 Complement the class diagrams which represent structure.
 Useful to find participating objects.
 Time consuming to build but worth the investment.

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”)
 Two types of states:
 Action state:
 Cannot be decomposed any further
 Happens “instantaneously” with respect to the level of abstraction
used in the model
 Activity state:
 Can be decomposed further
 The activity is modeled by another activity diagram

Activity Diagram: Modeling Decisions

Activity Diagrams: Modeling Concurrency
 Synchronization of multiple activities
 Splitting the flow of control into multiple threads
Synchronization
Splitting
Archive
Incident
Open
Incident
Document
Incident
Allocate
Resources
Coordinate
Resources

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

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
 We concentrate only on a few notations:
 Functional model: use case diagram
 Object model: class diagram
 Dynamic model: sequence diagrams, statechart and activity
diagrams

ch2lect.ppt

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