SWT Diagrammatics

1
SWT - Diagrammatics

• Lecture 3/4 - Diagramming in OO Software
  Development - partA
• 2-May-2000

2
Previous Lecture Review

• Diagram Distinctions
• Adjoinment, Linkage, Containment.
• Diagram Taxonomies.
• Diagram use in Computer Science
• Venn, Flowcharts, NSDs, Structure, Dataflow,
  ERDs, Cell and Arrows, State, Petri nets.
• Logic Gate Diagrams.
• How to operate Theseus under CM.

3
Overview

• OO Introduction,
• OO Design Notations,
• Objects, Messages / Control Data Flow, Classes.
• Class Attributes and Operations,
• Visibility of Attributes and Operations,
• Relationships
• Association, Multiplicity, Aggregation,
• Dependency, Inheritance.
• Object Oriented Views

4
What OO Systems are?

• OO Systems are viewed as compositions of domain
  specific object abstractions, rather than data
  and functions. Objects associate data and
  behaviour.
• Objects in a System inter-communicate by sending
  messages to each other.
• An Object is a domain
  concept that
  has
• State
• Behaviour
• Identity

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OO Software Engineering

• has three distinctive OO processes
• OO Analysis (OOA) focuses on the understanding
  of real-world models.
• OO Design (OOD) stresses the mapping of the OOA
  model to structured architectures, and
• OO Programming (OOP) deals with the building of
  OOD models under the constraints of the existing
  environments.

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The Object Model

Is a view of the world in terms of Objects and
their relationships.
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Object Oriented Design Notations

• OOD is one of CSs disciplines that make heavy
  use of diagrams.
• There are many different OOD notations, all
  conveying the same (more or less) information
  about the systems they describe
• Coad/Yourdon, Fusion, Jacobson, Martin/Odell,
  Shlaer and Mellor, Wirfs-Brock et al, Meyer etc
• Three are the most popular ones
• Booch,OMT, UML.
• You can use which ever you prefer, however UML
  became the standard in OO design on feb97.

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Objects

• An object is an atomic entity, formed from the
  union of state and behaviour.
• Provides encapsulation.
• Provides a weak coupling with the outside world.
• Software objects define an abstract
  representation of real or virtual world entities.

Visible behaviour
An object
Hidden internal state
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Objects

• In Booch, objects are represented by clouds.
• In OMT as in UML, objects are represented by
  rectangles.
• In UML, the name of the object is underlined.

Booch OMT
UML
Name Class
Name Class
Name Class
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Messages / Control Data Flow

• The message is the unit of inter-object
  communication.
• It allows interaction in a flexible manner.
• It is responsible for the delegation of tasks,
  and guarantees that constraints are satisfied.
• A message combines control flows and data flows
  within a single entity.
• The notion of a message is an abstract concept
  it could be a constructor, a method call, a
  discrete event, an interrupt, a UDP datagram etc.

Message A
Control Flow
Object1
Object2
Data Flow
Data Flow
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Messages / Control Data Flow

• In the three notations, messages are represented
  using arrows near the links.
• The control flow type is represented by using a
  line decorated with an arrowhead.
• A small circle connected to the line indicates a
  data flow, with the arrow pointing to the
  direction of the flow.
• This notation is optional and has become
  redundant.

Booch OMT
UML
Data flow represented by the message labels
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Classes

• A class is the product of an abstraction process
  which starts with the identification of common
  characteristics of a set of elements, and
  proceeds to the concise description of these
  characteristics.
• The abstraction process is arbitrary it is
  defined with respect to a particular viewpoint

A Class
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Classes

• A class describes the definition domain of a set
  of objects.
• It acts as a mould from which objects can be
  created.
• Software objects are built from the class, via a
  process called instantiation, objects are
  instances of classes.
• In Booch, classes are represented using dotted
  clouds.
• In OMT, as in UML, classes are represented using
  rectangles.

Booch OMT
UML
Class
Class
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Class Attributes and Operations

• Each class is represented as a rectangle
  subdivided into three components
• The name of the class,
• The attributes of the class,
• The operations of the class,
• By default, attributes are hidden and operations
  are visible.
• These compartments may be omitted to simplify the
  diagrams.

Class name
Attributes
Operations( )
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Class Attributes and Operations

• In all three notations, attributes and operations
  are represented within the class glyph.
• Some attributes can be hidden for the sake of
  readability.
• OMT and UML use boxes to distinguish the
  attributes from the operations.

Booch OMT
UML
Class name
Class name
Class name
Attributes
Attributes
Attributes
Operations( )
Operations( )
Operations( )
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Visibility of Attributes and Operations

• Visibility rules complement and refine the
  concept of encapsulation.
• It is possible to customise the degree of
  protection to the benefit of a class client by
  declaring attributes as public, protected or
  private.
• One of the benefits of breaking encapsulation can
  be, for example, to reduce the time required to
  access attributes by making unnecessary to call
  setters/getters. Could this be a right decision?

Class name
Public Attribute Protected Attribute -
Private Attribute
Public Operation( ) Protected Operation( ) -
Private Operation( )
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Visibility of Attributes and Operations

• The three notations encompass public, protected
  and private levels of protection.
• Booch provides an additional implementation
  level.

Booch OMT
UML
Nothing public protected private
implementation
Nothing unspecified public protected -
private
public protected - private
Class name
Class name
Class name
Public Attribute Protected Attribute -
Private Attribute
Public Attribute Protected Attribute -
Private Attribute
Public Attribute Protected Attribute
Private Attribute
Public Operation( ) Protected Operation(
) Private Operation( )
Public Operation( ) Protected Operation( ) -
Private Operation( )
Public Operation( ) Protected Operation( ) -
Private Operation( )
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Relationships Association

• The association relationship expresses a
  bi-directional, semantic connection between
  classes.
• An association is an abstraction of the links
  that exist between object instances.
• It is possible to specify the role of a class
  within an association.
• A role name may be specified on either side of
  the association.

University
Student
Dean
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Relationships Association

• In all the three notations, an association is
  represented by a continuous line between the
  classes that participate in it.

Booch
OMT UML
Student
University
University
Student
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Multiplicity

• Relationships between classes carry multiplicity
  information that specifies the number of
  instances that participate in the relationship
• The table below summarises the most common
  multiplicity values
• Symbol Meaning
• 1 One and only one
• 0..1 Zero or one
• M..N From M to N (natural integers)
• From zero to any positive integer
• 0.. From zero to any positive integer
• 1.. From one to any positive integer

University
Student
1 0..
1 1
Dean
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Multiplicity

• OMT proposes a graphical representation based on
  circles.
• Take care not to confuse these circles with those
  meaning has and uses in Booch, as there is no
  relationship between these two representations.

Booch OMT
UML
1 by default
1 0..1 N 3..5, 7, 15 3..N
0..N
1 0..1 3..5, 7, 15 3..
0..1
1
3..5
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Relationships Aggregation

• An aggregation is a particular kind of
  association that expresses a stronger coupling
  between classes.
• Aggregation allows the representation of
  relationships like master and slave, all and
  part of and composed of and components.
• It is commonly referred to as a HasA (or
  HasMany) relationship.

Car
Engine
1
1
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Relationships Aggregation

• There is no strict equivalence between the Booch,
  OMT and UML notations.
• As aggregation is concerned, Booch is closer to
  the design phase, OMT is closer to the analysis
  stage, and UML covers both.
• 2 cases are illustrated for each design
  methodology aggregation by reference and
  aggregation by value (same in OMT)

Booch OMT
UML
Car
Engine
Car
Engine
Car
Engine
Car
Engine
Car
Engine
Car
Engine
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Relationships Dependency

• A dependency is a loose association that
  expresses a weaker coupling between classes.
• Usually dependency shows that a class uses
  another class with one way or another, maybe by
  using the other classs static methods or by
  passing objects of the second classs type to
  another object of another class.
• It is commonly referred to as a Uses
  relationship.

Assembler Robot
Car Parts
1
1..
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Relationships Dependency

• Booch represents a dependency using an
  association labelled with a small circle placed
  on the client side.
• OMT represents a dependency using a dotted arrow
  with a filled head.
• UML uses a dotted arrow with an open head.
• In OMT and UML the arrow points to the supplier
  the element being dependent on.

Booch OMT
UML
Robot
Parts
Robot
Parts
Robot
Parts
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Relationships Inheritance

• Inheritance is a technique offered by programming
  languages to construct a class from one or more
  (in C) classes, sharing attributes, operations
  and sometimes constraints within a hierarchy of
  classes.

• A class can specialise, extend, subclass, or be a
  child of another class.

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Relationships Inheritance

• Inheritance propagates the characteristics of the
  parent class (depending on their visibility) into
  the child classes.
• It is commonly read as an IsA relationship.

Vehicle
Car
Bike
Audi
BMW
Yamaha
Suzuki
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Relationships Inheritance

• In all three notations, inheritance is
  represented using an arrow that points from the
  subclass to the superclass.

Booch OMT
UML
Vehicle
Vehicle
Vehicle
Car
Car
Car
Vehicle
Vehicle
Vehicle
Bike
Car
Bike
Car
Car
Bike
Or as in OMT
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Object Oriented views

• Hierarchy view (usually static)
• classes, interfaces and their relationships.
• Interaction view (usually dynamic)
• objects, method calls, events, messages.
• Modules view
• name spaces, packages-libraries-modules, classes,
  and their internal and external dependencies.

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Hierarchy View
TestProgram
has
Drawable
implements
main()
draw()
Shape
draw()
setOrigin()
setColor()
Relationships
is

• Inheritance,
• Aggregation,
• Uses.

Rect
Oval
Line
draw() toString() setText()
draw() toString() setText()
draw() toString() setText()
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Interaction View
myTestprogram
myVector
myEnum
myShape
drawAll()
elements()
hasMoreElements() nextElement()
draw()

• Is based on objects and method calls.
• Depicts the runtime of the system.

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Module View
figures
tools
framework
commands
domain
gui
util

• Package Visibility
• Package Dependencies

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The end of lecture 3