8 oo approach&uml-23_feb

Object Oriented
Modeling
A Concept Tutorial

The need
• Corporations are becoming
information based
organizations
• Volume of information is
expanding faster than the
capacity to process it
• Where does the fault lie?
– Computers are faster and
more powerful than ever
before!
• The Software Crisis!!

Reasons for the Crisis
• Complexity
– requirements are demanding and of contradictory nature
• functionality
• usability
• cost
• reliability
• performance
• longevity
– requirements change during development
– problem domains can be complex
– Managing the development process is not easy
– impedance mismatch between user and developer

Divide and Rule!
• “The technique of mastering complexity is known since ancient
times: Divide and Rule”
….Dijkstra

Solutions
• Building better Software is a major
challenge!!
• ModularProgramming
Modularization of Procedures and data
– Modularization of procedures
– Subroutines
– Structured Programming
- Functional decomposition-
componentization
– Computer Aided Software
Engineering ( CASE)

…Solutions
- Modularization of data:
-each subroutine can contain its own data
-data can be stored in external files
-database management systems
( DBMSs)
– Hierarchic model - tree structures
– network model - data
interconnected freely, no tree
structure necessary
– relational model - data stored in
simple tables
Clearly a new approach must be
considered!

Algorithmic/ Functional Decomposition
• Define the how and what of the goal
• Specifying and decomposing the system functionality
• Decompose each task into smaller tasks - ( subroutines…
language statements)
• Implement the program and the steps that decompose each
function
Risk:
Seems like the most direct way of doing things, but resulting
system may be fragile, requirements change may necessitate
massive restructuring

Object Oriented Decomposition
• Decomposing a system into objects, the basic components and
design
• managing complexity inherent in the real world problem by
abstractions ( of knowledge) and encapsulation (of information
and behavior) within objects

The Object Oriented
Approach
• Three keys to the OOtechnology:
– Objects
– Messages
– Classes

Objects
• Software package that contains a
collection of related Procedures and
Data
– Procedures : Methods
– Data elements : Variables
- Ideal Modules: Objects can be defined and
maintained independently
E.g. Vehicle
- Everything an Object” knows” is expressed
in its variables and everything it can “ do” is
expressed in its methods- Encapsulation
Methods
Variables
( DATA MEMBERS)

Classes
• There may be many objects of a
given type - extremely inefficient to
redefine the same methods in every single
occurrence of that object
• A Class is a Template that defines
methods and variables to be
included in a particular type of
object
• Objects that belong to a Class are
Instances of the Class
Class
Methods
Variables
(Data members)
Values

Classes VS. Objects
Class Object
Class is a type/ template
for similar objects
Object is an instance of
the class
Class is purely a static
concept, represented by
program text
Objects are run time /
dynamic entities that
occupy space in memory

Classes VS. Objects
Example
class EMPLOYEE // EMPLOYEE is a class
{
char name[30];
void putname(char*n);
void prinname();
}
main()
{
EMPLOYEE emp; // emp is an object
emp.putname(“myname”;
emp.printname();
}

An Analogy
• Cells are ( organic)
“packages” , like Objects,
that combine information
(data) and behavior
-Encapsulation!!
• Cells, like Objects
communicate through
Messages( chemical).
• Cells are (natural) building
blocks- organized in a
Hierarchy of specialized
types and subtypes
Nucleus
Membrane
Mitochondria( Energy Converters)
Endoplasmic Reticulum
(Protein Factory)

Objects as Abstract
Data Types
• OO technology supports data
abstraction.
• An abstract data type consists of a new
class assembled from built in data types,
such as numbers and characters
Abstract Data Type
Built in Data Types

OO Themes
Major themes •Abstraction
•Encapsulation
•Hierarchy/ Inheritance
•Polymorphism
•Modularity
Minor themes •Typing
•Persistence
OO modeling involves consideration of these themes.

Abstraction
An abstraction denotes the essential characteristics of an object
that distinguishes it from other kinds of objects.
• Note essential details
• ignore irrelevant details
to manage complexity

..Abstraction
• EMPLOYEE
Human Resources
System
Payroll System
Name
Designation
Qualification
Skills
.
.
.
Name
Salary
HRA
Conveyance
.
.
.

Encapsulation
• Promotes hiding of information
- Objects do not “touch” each other’s data
• Facilitates Changes
- Effects of change are limited to a few
classes
CAPACITY
LOAD
LIFT
LOAD
CONTENTS
MoveTo
UNLOAD

Encapsulation
• Act of grouping into a single object - both data and operations
that affect the data
• Apportions complexity of the system to individual , pertinent
objects
• Knowledge encapsulated within an object is “hidden” from an
external view
• An object has a public interface and a private representation

Accessing Objects-Messages
• Interactions between Objects
- Message from a sender
object asks the receiver
object to execute its method.
Authors of Simula offered this solution
• Typical Structure:
– Object Name - Method-
Parameter
• Example ; “Receiver-MoveTo-
Destination”
RECEIVER
MoveTo
LOAD
LIFT
SIZE
SPEED
CAPACITY
CONTENTS
SENDER
“Receiver MoveTo Destination”

STEP 1:
• Sender ( e.g. client) requests a service by sending “message”
• Message does not specify how the operation is to be performed
STEP 2:
• Receiver ( e.g. server) responds by executing a “method”
• Optionally sends some information back to the sender
Accessing Objects-Messages

Messages
• Objects interact through messages
• A message has three parts;
{Receiver} { Method} {Parameter}
The response to a message is called a
Return value
TOTAL
SENDER
RECEIVER
Purchase order100
Rs. 1 crore
“Rs. 1 crore”
“ Purchase order_ 100 TOTAL”

Types of interfaces
• Private:
A declaration that forms a part of the interface of a class and is not
visible to other classes
• Public:
A declaration that forms a part of the interface of a class and is
visible to clients

Inheritance
• A mechanism by which one class
of objects can be defined as a
special case of a more general
class
– Superclass - subclasses
• A subclass inherits all the methods
and variables of its superclass
Subclass- Motor
Superclass- Auto Part
Subclass- Chassis

Hierarchy
• Classes can be nested to any
degree, inheritance will
automatically accumulate down
through all the levels
of the tree structure
Connector
….
Auto Part
Motor Chassis
Stepping motor Drive motor
Variable speed
Drive motor
Fixed speed
Drive motor
….
.
.
.
.
.
.

..Inheritance
• When a class Y inherits from class X:
– X is the base or Super class
– Y is the derived or Sub class
• Y contains
– The part derived from X
– new code specific to Y

Classes
• Classes allow a programmer to
organize complex systems in a
rational, orderly way.
• When an instance ( object)
receives a message, it refers to
its Class for its methods and
variable types and then applies
these to its own unique set of
values
Look up method and variable definition in the Class
DRAW
DRAW
DRAWTOOL
DRAWTOO104L
TRIANGL
E
“DRAWTOOL104 DRAW:TRIANGLE”
Use values contained in the instance

Class Hierarchies
• An object will search its
Superclass for methods
and variables
• This leads to efficient packaging
of information.
“A PRINT” INSTANCE”
Not here
Not here
Found it!!

..Inheritance
Example:
Define a class describing polygons:
• Attributes - vertices
• Operation - translation, rotation, display, computation of
perimeter

..Inheritance
• If we need a new class representing Rectangle, we can derive it
from the class representing Polygon
Common features Special features
Translation, rotation,
display
Number of vertices, angle
between sides, special
formula to compute
perimeter

..Inheritance
Pseudo- code forrectangle:
class Rectangle inherits Polygon
{
redefines perimeter() from Polygon
and
has features specific to Rectangle
}

Polymorphism
• Hiding Alternative procedures behind
a common interface is called
Polymorphism
• e.g. The name “DRAW” can be used
for all the variations of the method-
such as “DRAW CIRCLE” and “DRAW
RECTANGLE”.
DRAW DRAW DRAW
“SHAPE DRAW”
A DRAWmethod in multiple
objects:

.. Polymorphism
• The function “ DRAW” is declared in the base class Polygon
• The function can be redefined in derived classes to describe
specific action/ operation to be performed
• Same function name DRAW is used in all the derived classes
• The version of DRAW function to be used is decided during
runtime by the object

Goals that guide Class Hierarchies
• Build general purpose classes for reuse
• make change easier
• correctly reflect the real world system
• TO BUILD SOLID WORKING MODELS

Modularity
A modularsystemis a system decomposed into a set
of cohesive and loosely decoupled modules
Example:
Insurance Policy, claim processing, accounts, scheme
builder

Typing
• Typing is enforcement such that objects of different
types may not be interchanged, or, at most may be
interchanged only in very restricted ways
• Strongly typed languages require type checking of
all arguments
• Static type checking occurs at compile time
• Dynamic type checking occurs at execution time
• Strong typing avoids run time errors
• Type declarations serve as program documentation

Persistence
• This is a property by virtue of which
– object continues to exist afterits creatorceases
to exist

Promise of the OO Approach
• Conventional software
– solves a specific problem
– is built from scratch
• Object Oriented software
– models a system
– is built by assembly.
• modeling has many advantages.
– understandability
– flexibility
– Longevity

Industrialization of
Software
• A striking parallel exists
between the OO approach and
the Industrial revolution-
– Handcrafting ---> Mass
Production - Paradigm
shift!!
• The goal is Industrial
revolution forSoftware
• The success depend on
development of reusable,
standard objects.
• The Challenge lies in getting
the Classes right.
A Class manufacturing instances

Unified Development Process
(UDP)
• UDPis a method of managing OOSoftware Development
• It can be viewed as a Software Development Frameworkwhich
is extensible and have features to do the following:
– Iterative Development
– Requirements Management
– Component-Based Architectural Vision
– Visual Modeling of Systems
– Quality Management
– Change Control Management

UDP Features
• Templates forall majorartifacts, including:
– RequisitePro templates (requirements tracking)
– Word Templates forUse Cases
– Project Templates forProject Management
• Process Manuals describing key processes
• Online Repository of Process Information and Description

An Iterative Development Process...
• Recognizes the reality of changing requirements
– Caspers Jones’s research on 8000 projects
• 40% of final requirements arrived afterthe analysis phase, after
development had already begun
• Promotes early riskmitigation, by breaking down the systeminto mini-projects
and focusing on the riskierelements first
• Allows you to “plan a little, design a little, and code a little”
• Encourages all participants, including testers, integrators, and technical writers
to be involved earlieron
• Allows the process itself to modulate with each iteration, allowing you to
correct errors soonerand put into practice lessons learned in the prioriteration
• Focuses on component architectures, not final big bang deployments

An Incremental Development Process...
• Allows forsoftware to evolve, not be produced in one huge effort
• Allows software to improve, by giving enough time to the evolutionary process
itself
• Forces attention on stability, foronly a stable foundation can support multiple
additions
• Allows the system(a small subset of it) to actually run much soonerthan with
otherprocesses
• Allows interimprogress to continue through the stubbing of functionality
• Allows forthe management of risk, by exposing problems earlieron in the
development process

Goals and Features of Each Iteration
• The primary goal of each iteration is to slowly chip away at the risk facing the
project, namely:
– performance risks
– integration risks (different vendors, tools, etc.)
– conceptual risks (ferret out analysis and design flaws)
• Perform a “miniwaterfall” project that ends with a delivery of something tangible
in code, available for scrutiny by the interested parties, which produces
validation or correctives
• Each iteration is risk-driven
• The result of a single iteration is an increment--an incremental improvement of
the system, yielding an evolutionary approach

The Development Phases
• Inception Phase
• Elaboration Phase
• Construction Phase
• Transition Phase

Inception Phase
• Overriding goal is obtaining buy-in from all interested parties
• Initial requirements capture
• Cost Benefit Analysis
• Initial RiskAnalysis
• Project scope definition
• Defining a candidate architecture
• Development of a disposable prototype
• Initial Use Case Model (10% - 20% complete)
• First pass at a Domain Model

Elaboration Phase
• Requirements Analysis and Capture
– Use Case Analysis
• Use Case (80% written and reviewed by end of phase)
• Use Case Model (80% done)
• Scenarios
– Sequence and Collaboration Diagrams
– Class, Activity, Component, State Diagrams
– Glossary (so users and developers can speakcommon vocabulary)
– Domain Model
• to understand the problem: the system’s requirements as they exist within the
context of the problemdomain
– RiskAssessment Plan revised
– Architecture Document

Construction Phase
• Focus is on implementation of the design:
– cumulative increase in functionality
– greater depth of implementation (stubs fleshed out)
– greater stability begins to appear
– implement all details, not only those of central architectural value
– analysis continues, but design and coding predominate

Transition Phase
• The transition phase consists of the transferof the system to the user
community
• It includes manufacturing, shipping, installation, training, technical support
and maintenance
• Development team begins to shrink
• Control is moved to maintenance team
• Alpha, Beta, and final releases
• Software updates
• Integration with existing systems (legacy, existing versions, etc.)

Elaboration Phase in Detail
• Use Case Analysis
– Find and understand 80% of architecturally significant use cases
and actors
– Prototype User Interfaces
– Prioritize Use Cases within the Use Case Model
– Detail the architecturally significant Use Cases (write and review
them)
• Prepare Domain Model of architecturally significant classes, and identify their
responsibilities and central interfaces (View of Participating Classes)

What is UML?
Modeling involves
• understanding ( semantics) a subject (system)
and
• capturing and communicating this knowledge
The Unified Modeling Language ( UML) is:
• A complete language for capturing knowledge (semantics) about a
subject (system) and communicating the knowledge (syntax)
– the result of unifying the IT industry’s best engineering practices
– proposed by Booch, Rumbaugh and Jacobson-the Three Amigos

..What is UML?
• UML is the standard language for visualizing, specifying,
constructing, and documenting the artifacts of a software
intensive system
• It can be used with all processes, throughout the development
life cycle, and across different implementation technologies
• Applicable to not only Software Systems but to any other type of
systems

Evolution of the UML
• Unification
– Jim Rumbaugh, Grady Booch and Ivar Jacobson joined Rational
Software Corporation to unify their methods.
• Rumbaugh - Analysis oriented (OMT)
• Booch - Design and Construction oriented
• Jacobson - Use case oriented (OOSE)
– Since the independent methods were evolving towards one
another, continue evolution by unification.
– Identify and incorporate fundamental concepts, building a meta
model and a notation to describe them.

Standardization
• More companies joined the UML partner’s consortium to
contribute their ideas and produce version 1.1 of the UML with
– Increased formalism
– Improved structural packaging
– Improved mapping of notation to semantics
• UML 1.1 is accepted by OMG as a standard in fall 1997.
• Current version UML 2.0

History of the UML
Nov ‘97 UML approved by the OMG

Scope of UML
• Fusing concepts of Booch, OMT and OOSE.
• Focusing on a standard modeling language (common notation
and semantics)
• Incorporating the object-oriented community’s consensus on
core modeling concepts.
• Providing sufficient notation to address contemporary modeling
issues directly and economically.
• Providing extensibility mechanisms to extend UML for individual
projects.

– The UML enables and promotes a use-case-
driven, architecture-centric, iterative, and
incremental process that is object oriented and
component based.

The UML Definition
• Defined by a set of documents
– UML Semantics
– UML Notation Guide

The UML Semantics Document
• Constitutes the single, common, formal and comprehensive
specification of the UML (inside vie w).
• Primarily used by tool vendors.
• Specifies the UML’s layered architecture, organization and
defines modeling elements.
• Enables consistent usage of the UML.

The UML Notation Guide
• Constitutes the notational or visual representation of the UML
and provides examples (o utside vie w)
• Primarily used by practitioners applying the UML
• Specifies UML diagrams and their modeling elements

Model Views and UML Diagrams
•Use Case
UserView
Behavioral View
•Sequence
•Collaboration
•State Chart
•Activity
Structural View
•Class
•Object
Implementation View
•Component
Environment View
•Deployment
User view
* Use
case

UML Diagrams
• Class diagram
For a view of the static structure of the system
• UseCase diagram
For High level business scenarios
• Sequence diagramorCollaboration diagram
For detailed activities within a scenario
• State chart diagramorActivity Diagram
For classes with a dynamic behavior
• Component diagrams
For describing organization and dependencies among software
components
• Deployment diagrams
For describing the configuration of resource elements and
mapping of software implementation components on to them
• Package diagram
For Modules

Library Management System- A Case Study
The Library has:
• three categories of members
• a librarian and assisting staff
• an accounts section
The Library Management System should provide the following
functionality:
• borrowing and returning of books
• querying, reserving and recommending books
• acquiring books
• issuing overdue notices to members

..Class Diagram
• Shows the static structure of the system - classes and their
relationships
• Classes
– structure (attributes)
– behavior (operations)
• Relationships
– Association, aggregation, dependency, and inheritance
– Multiplicity and navigation indicators
– names

4
5
Class Diagram Notation
Class
Class with a compartment
Realizes Interface
Interface
Constraint
N-ary Association
Binary Association
1
2
3
4
5
6
7

Library
Book
no
VisibilityAttribute TypeScopeInitVal
Title a
Author a
Publisher a
Subject a
Keywords a
edition a
Price a
CopyInLib
isReference a
accessionNo a
isIssued a
copyNo a
Librarian
LibraryMember
name a
memberId a
Accountant
OrderInfo
supplierId a
NoOfCopies a
hasBooks1
*
hasCopies
1
*
hasLibrarian
1
1
borrows1
0..5
hasMembers
1
0..200
orders
1
*
Class Diagram

Relationships
• An association is a bi-directional connection between classes
– An association is shown as a line connecting the related classes
• An aggregation is a stronger form of relationship where the relationship is between a whole and its
parts
– An aggregation is shown as a line connecting the related classes with a diamond next to the
class representing the whole
• A dependency relationship is a weaker form of relationship showing a relationship between a client
and a supplier where the client does not have semantic knowledge of the supplier
• A dependency is shown as a dashed line pointing from the client to the supplier

Relationships - contd..
• An association class is an association that also has class properties(or a
class has association properties)
• A constraint is a semantic relationship among model elements that
specifies conditions and propositions that must be maintained as true:
otherwise, the system described by the model is invalid
• An interface is a specifier for the externally visible operations of a class
without specification of internal structure. An interface is formally
equivalent to abstract class with no attributes and methods, only abstract
operations.
• A qualifier is an attribute or set of attributes whose values serve to
partition the set of instances associated with an instance across an
association.

Association
Teacher
Navigation
Aggregation
Student
Guide RS
1 Guides *
Teacher
DepartmentInstitute
1 *

Composition
Page Frame
1 *
Page Frame
1 *
Page Frame
1 *
Window
Header SliderMenu

Dependency
Window Button
uses
SalaryEmployee
access

Association Classes
CourseTeacher
Offering
No of students
Venue
Slot number
1 Teaches *
Company Employee
Job
Designation
Salary
1 employs *

Constraint
CommitteeFaculty
* Member of *
1 Head of *
{ subset }
Realization
AccountImpl
<interface>
Iaccount
Deposit()
withdraw()

Qualifier
Bank
Customer
Account #
*
*
Factory
Itemproduced
Item #
*
1

…Use Case Diagram
• Represent the interaction between users and the
system
• Identifies users (roles) and external systems
• Determines the functional scope of the package
(module)

Use Case Diagram Notation
Actor
Association
Use Case
Use case with Extension points
<<Uses>>
<<Extends>>

..State Chart Diagram
A state chart (transition) diagramis used to show
– The life history of a given class, UseCase, operation
– The events that cause a transition from one state to another
– The actions that result from a state change
State transition diagrams are created for objects
with significant dynamic behavior

Interaction Diagram
• Interaction diagrams describe how use cases are realized as
interactions among objects
• Show classes, objects, actors and messages between them to
achieve the functionality of a
UseCase
• Two types of interaction diagrams
– Sequence diagrams
– Collaboration diagrams

..Sequence Diagram
• Is used to elaborate a use case
• Describes a scenario - it is normal that a use case has multiple
scenarios
• Helps to describe the expected system behavior to a user
• Follows an event from inception to completion of processing by
the system

Sequence Diagram Notation
Actor
Class
Synchronous message
Asynchronous message
Return message
Focus of Control
lifeline
Termination

Sequence Diagram
Library
member UI Member Book Copy

..Collaboration Diagram
• describes interactions among Classes ( objects)
• can be drawn instead of a sequence diagram
• Message sequencing is shown using sequence numbers

Collaboration Diagram Notation
Class
Messages with
sequence
numbers
( “Collaborates
with Class”)
Actor

..Activity Diagram
Activity diagrams are similar to State Chart diagrams.
However they describe the behavior of a Class in
response to internal processing.
• Transitions are triggered by completion of activity
• For describing behavior of Use Cases or operations

..Component Diagram
• Describe organization and dependency between the software
implementation components
• Components are distributable physical units -e.g. source code,
object code.

Component
Dependency
Component Diagram Notation

..Deployment Diagram
• Describe the configuration of processing resource elements and
the mapping of software implementation components onto them
• contain components - e.g. object code, source code, and nodes -
e.g. printer, database, client machine

Deployment Diagram Notation
Component
Interface
Dependency
Node
Connector

Deployment Diagram
LibClient2
ClientLibrarian
LibClient1
LibServer
LibMgmtSys
ClientMember
tcp-ip tcp-ip

…Package Diagram
A Package is :
• an application view
• exploded into a set of modules
• linked to the diagrams that model that application view

Package Diagram Notation
Container package
Package
Dependency
Generalization

How to perform Modeling Process?
• Break up the system into packages. Draw a high level Package
Diagram for the system.
• Draw Use Case diagrams for each package
• Analyze each use case in detail - identifying variations, common
use cases, scenarios of interest
• Draw a Sequence /Collaboration diagram for each scenario

.. Modeling Process
• Draw a Class Diagram for each package
– classes will be shared across the entire application model
– a class will be owned by a “package” - others will use it
• Refine the inheritance hierarchy (this will be across the
application)
• Identify attributes and keys for the classes

..Modeling Process
Draw
• State Chart Diagrams or Activity Diagrams for classes that exhibit a
significantly dynamic behavior
• Component Diagrams to elucidate the intercomponent dependencies
• Deployment Diagrams to describe the configuration of resource
elements and mapping of the software implementation components
onto them

Overview of Modeling Process
Application Package Diagram
Component Diagram
Deployment Diagram
Use Case Diagram
Sequence Diagram
Collaboration Diagram
Activity Diagram
Class Diagram
State Chart Diagram

Use Case Template
• Overview
• Actors
• Stimulus
• Pre and Post Conditions
• Normal Flow
• Logic
• Alternate flow(s)
• Exception(s)
• Extends
• Uses
• Unresolved Issues
• Non functional requirements
• Future requirements

Use Case Analysis
• What is a Use Case?
– A sequence of actions a system performs that yields a valuable
result for a particular actor.
• What is an Actor?
– A user or outside system that interacts with the system being
designed in order to obtain some value from that interaction
• Use Cases describe scenarios that describe the interaction between users of the
system and the system itself.
• Use Cases describe WHAT the system will do, but never HOW it will be done.

What’s in a Use Case?
• Define the start state and any preconditions that accompany it
• Define when the Use Case starts
• Define the order of activity in the Main Flow of Events
• Define any Alternative Flows of Events
• Define any Exceptional Flows of Events
• Define any Post Conditions and the end state
• Mention any design issues as an appendix
• Accompanying diagrams: State, Activity, Sequence Diagrams
• View of Participating Objects (relevant Analysis Model Classes)
• Logical View: A View of the Actors involved with this Use Case, and any Use Cases used
or extended by this Use Case

Use Cases Describe Function not Form
• Use Cases describe WHAT the system should do, but never
HOW it will be done
• Use cases are Analysis products, not design products

Benefits of Use Cases
• Use cases are the primary vehicle for requirements capture in UP
• Use cases are described using the language of the customer (language of the
domain which is defined in the glossary)
• Use cases provide a contractual delivery process (UP is Use Case Driven)
• Use cases provide an easily-understood communication mechanism
• When requirements are traced, they make it difficult for requirements to fall
through the cracks
• Use cases provide a concise summary of what the system should do at an
abstract (low modification cost) level.

Difficulties with Use Cases
• As functional decompositions, it is often difficult to make the transition from
functional description to object description to class design
• Reuse at the class level can be hindered by each developer “taking a Use Case
and running with it”. Since UCs do not talk about classes, developers often wind
up in a vacuum during object analysis, and can often wind up doing things their
own way, making reuse difficult
• Use Cases make stating non-functional requirements difficult (where do you say
that X must execute at Y/sec?)
• Testing functionality is straightforward, but unit testing the particular
implementations and non-functional requirements is not obvious

Use Case Model Survey
• The Use Case Model Survey is to illustrate, in graphical form, the
universe of Use Cases that the system is contracted to deliver.
• Each Use Case in the system appears in the Survey with a short
description of its main function.
– Participants:
• Domain Expert
• Architect
• Analyst/Designer (Use Case author)
• Testing Engineer

Analysis Model
• In Analysis, we analyze and refine the requirements described in the Use Cases in order to
achieve a more precise view of the requirements, without being overwhelmed with the
details
• Again, the Analysis Model is still focusing on WHAT we’re going to do, not HOW we’re
going to do it (Design Model). But what we’re going to do is drawn from the point of view of
the developer, not from the point of view of the customer
• Whereas Use Cases are described in the language of the customer, the Analysis Model is
described in the language of the developer:
– Boundary Classes
– Entity Classes
– Control Classes

Why spend time on the Analysis Model, why not just “face the
cliff”?
• By performing analysis, designers can inexpensively come to a better understanding of
the requirements of the system
• By providing such an abstract overview, newcomers can understand the overall
architecture of the systemefficiently, froma ‘bird’s eye view’, without having to get
bogged down with implementation details.
• The Analysis Model is a simple abstraction of what the systemis going to do fromthe
point of view of the developers. By “speaking the developer’s language”, comprehension
is improved and by abstracting, simplicity is achieved

Boundary Classes
• Boundary classes are used in the Analysis Model to model interactions between the system
and its actors (users orexternal systems)
• Boundary classes are often implemented in some GUI format (dialogs, widgets, beans,
etc.)
• Boundary classes can often be abstractions of external APIs (in the case of an external
systemactor)
• Every boundary class must be associated with at least one actor:

Entity Classes
• Entity classes are used within the Analysis Model to model
persistent information
• Often, entity classes are created from objects within the
business object model or domain model

8 oo approach&uml-23_feb

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8 oo approach&uml-23_feb