Chapter 2: Modeling with UML 2

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• Chapter 2 Modeling with UML - 2

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A Medical Clinic Example
A patient calls the clinic to make an
appointment for a yearly checkup. The
receptionist finds the nearest empty time slot in
the appointment book and schedules the
appointment for that time slot
A patient can request or discuss medication with
a doctor
A patient can make payment through the system
ltincludesgt, ltextendsgt, generalization
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Use Case Diagrams Summary

• Use case diagrams represent external behavior
• All use cases need to be described for the model
  to be useful.
• 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)
• ltltincludesgtgt and ltltextendsgtgt allow common
  fragments of use cases to be pulled out into a
  separate use cases
• ltltincludesgtgt is like a use case subroutine
• ltextendsgtgt is an alternative course of action

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Class Diagrams
Enumeration getZones() Price getPrice(Zone)

• 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.

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Classes
Name
Signature
Attributes
Operations

• 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.

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Instances
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.

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Actor vs Instances

• What is the difference between an actor , a
  class and an instance?
• Actor
• An entity outside the system to be modeled,
  interacting with the system (Passenger)
• Class
• An abstraction modeling an entity in the problem
  domain, must be modeled inside the system
  (User)
• Object
• A specific instance of a class (Joe, the
  passenger who is purchasing a ticket from the
  ticket distributor).

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Associations
Enumeration getZones() Price getPrice(Zone)
PriceZone

• Associations denote relationships between
  classes.
• The multiplicity of an association end denotes
  how many objects the source object can
  legitimately reference.

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1-to-1 and 1-to-many Associations
Country
capital
nameString
nameString
One-to-one association
Point

Polygon
x Integer
y Integer
draw()
One-to-many association
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Many-to-Many Associations
Lists


Company
StockExchange
tickerSymbol
1

Lists
Company
StockExchange
SX_ID
tickerSymbol
qualifier
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From Problem Statement To Object Model

Pr
oblem Statement A stock exchange lists many
companies. Each company is uniquely identified
by a ticker symbol
Class Diagram
Company


StockExchange
Lists
tickerSymbol
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From Problem Statement to Code
Pr
oblem Statement

A
stock exchange lists many companies.
Each company is identified by a ticker Symbol
Class Diagram


Company
StockExchange
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()

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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
0..2
1
Muffler
Tailpipe
diameter
diameter
3
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Inheritance

• The children classes inherit the attributes and
  operations of the parent class.
• Inheritance simplifies the model by eliminating
  redundancy.

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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.

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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.

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Qualifiers

• Qualifiers can be used to reduce the multiplicity
  of an association.

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Object Modeling in Practice Class Identification
Foo
Foo, by providing his customerId, can deposit,
withdraw, and get balance from his account.
CustomerId
Deposit()
Withdraw()
GetBalance()
Class Identification Name of Class, Attributes
and Methods
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Object Modeling in Practice Encourage
Brainstorming
Naming is important! Is Foo the right name?
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Object Modeling in Practice ctd
CustomerId
CustomerId
1) Find New Objects
2) Iterate on Names, Attributes and Methods
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Object Modeling in Practice A Banking System

Has
1) Find New Objects
2) Iterate on Names, Attributes and Methods
3) Find Associations between Objects
4) Label the assocations
5) Determine the multiplicity of the assocations
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Practice Object Modeling Iterate, Categorize!


Has
CustomerId
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Packages

• A package is a UML mechanism for organizing
  elements into groups (usually not an application
  domain concept)
• Packages are the basic grouping construct with
  which you may organize UML models to increase
  their readability.
• A complex system can be decomposed into
  subsystems, where each subsystem is modeled as a
  package

DispatcherInterface
Notification
IncidentManagement
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Class Diagram Summary

• Class diagrams represent the structure of the
  system
• Name, attribute, operation
• Class vs. instance
• Association, aggregation, composition,
  generalization
• Multiplicity

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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

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Nested messages
ZoneButton
Dataflow
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

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Iteration condition
continued from previous slide...
ChangeProcessor

Iteration
Condition
to be continued...

• Iteration is denoted by a preceding the message
  name
• Condition is denoted by boolean expression in
  before the message name

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Creation and destruction
continued from previous slide...
ChangeProcessor
Creation
Destruction

• 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.

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Sequence Diagram A Example
Making an online hotel reservation
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Sequence Diagram Summary

• UML sequence diagram represent behavior in terms
  of interactions.
• Useful to find missing objects.
• Time consuming to build but worth the investment.
• Complement the class diagrams (which represent
  structure).

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State Chart Diagrams
State
Initial state
Event
Transition
Final state
Represent behavior as states and transitions
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State Chart Diagrams -- Example

• A screen savor program

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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

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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
Closed
Active
Inactive
Archived
Incident- Documented
Incident- Archived
Incident- Handled
Activity Diagram for Incident (similar to
Moore (State Operation or Collection of
Operations)
Triggerless Transition
Completion of activity causes state transition
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Activity Diagram Modeling Decisions
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Activity Diagrams Modeling Concurrency

• Synchronization of multiple activities
• Splitting the flow of control into multiple
  threads

Splitting
Synchronization
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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
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What should be done first? Coding or Modeling?

• It all depends.
• Forward Engineering
• Creation of code from a model
• Greenfield projects
• Reverse Engineering
• Creation of a model from code
• Interface or reengineering projects
• Roundtrip Engineering
• Move constantly between forward and reverse
  engineering
• Useful when requirements, technology and schedule
  are changing frequently

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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

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Problems with UML

• Semi-formal
• Go directly to the class/objects a low level.
• Not good at express temporal information
  StateChart

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Models for Platos and Aristotles Views of
Reality
Plato
Aristotle

• Material reality is a second-class subordinate
  type of reality.
• The first-class type is a form Forms lie behind
  every thing or in the world. Forms can be
  abstract nouns like beauty or mammal or
  concrete nouns like tree or horse.
• There is an important difference between the
  world of forms and particulars. Forms are
  nonmaterial, particulars are material. Forms are
  permanent and changeless. Particulars are
  changing.
• Forms can be acquired intellectually through a
  dialectic process that moves toward the highest
  understanding of reality through the interaction
  of questions and answers.

• Aristotle accepted the reality of Forms as
  nonmaterial entities.
• However, he could not accept Platos idea, that
  these Forms were not real.
• Instead of two separate worlds, one for Forms and
  one for Particulars, Aristotle had only one
  world, a world of particular things.
• Particular things according to Aristotle have a
  certain permance about them, even while they are
  subject to change A tree changes colors without
  ceasing to be a tree. A horse grows in size
  without ceasing to be a horse.
• What is the root of this permancence? It is the
  things internal form, which minds detect, when
  they penetrate beyond the things changing
  attributes. So for Aristotle, reality is thus
  made up of particular things that are each
  composed of form antdn matter..

Using UML, we can illustrate Platons and
Aristotles viewpoints very easily and see their
differences as well
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Model for Platos View of Reality
Plato

• Material reality is a second-class subordinate
  type of reality.
• The first-class type is a form Forms lie behind
  every thing or in the world. Forms can be
  abstract nouns like beauty or mammal or
  concrete nouns like tree or horse.
• There is an important difference between the
  world of forms and particulars. Forms are
  nonmaterial, particulars are material. Forms are
  permanent and changeless. Particulars are
  changing.
• Forms can be acquired intellectually through a
  dialectic process that moves toward the highest
  understanding of reality through the interaction
  of questions and answers.

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Model Aristotles Views of Reality
Aristotle

• Aristotle accepted the reality of Forms as
  nonmaterial entities.
• However, he could not accept Platos idea, that
  these Forms were not real.
• Instead of two separate worlds, one for Forms and
  one for Particulars, Aristotle had only one
  world, a world of particular things.
• Particular things according to Aristotle have a
  certain permance about them, even while they are
  subject to change A tree changes colors without
  ceasing to be a tree. A horse grows in size
  without ceasing to be a horse.
• What is the root of this permancence? It is the
  things internal form, which minds detect, when
  they penetrate beyond the things changing
  attributes. So for Aristotle, reality is thus
  made up of particular things that are each
  composed of form antdn matter..

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Comparison of Platos and Aristotles Views
Aristotle
Plato