Transcript schach_sad_chap06b_20

Slide 6B.1
An Introduction to
Object-Oriented
Systems Analysis and Design
with UML and
the Unified Process
McGraw-Hill, 2004
Stephen R. Schach
[email protected]
Copyright © 2004 by The McGraw-Hill Companies, Inc. All rights reserved.
CHAPTER 6 — Unit B
Slide 6B.2
THE ANALYSIS WORKFLOW I
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Slide 6B.3
Continued from Unit 6A
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Fifth Iteration of the Initial Class Diagram (contd)
Slide 6B.4
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Dynamic Modeling
Slide 6B.5

Dynamic modeling is the third step in object-oriented
analysis

A statechart is constructed that reflects all the
operations performed by or to the information
system

The operations are determined from the scenarios
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The Concept of State

Slide 6B.6
The state of an information system is a particular set
of values of the attributes of that system
– The state is often represented by a specific screen

Each event causes the system to move from state to
state, that is, it causes a transition between states

Example: Microsoft Word
– The state is the current screen
– An event is to select (say) Font from the Format Menu
– The Font screen is then the new state
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Initial Dynamic Model: Osbert Oglesby

Initial statechart
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Slide 6B.7
Initial Dynamic Model: Osbert Oglesby (contd)
Slide 6B.8

The solid circle (top left) represents the initial state

The white circle with the small black circle inside
(top right) represents the final state

States other than the initial and final states are
represented by rectangles with rounded corners

The arrows represent transitions from state to state
– Example: The arrow from the initial state to the state
labeled Osbert Oglesby Information System Loop
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Initial Dynamic Model: Osbert Oglesby (contd)
Slide 6B.9

In state Osbert Oglesby Information System
Loop, one of five events can occur:
– Osbert can choose one of five options: buy a painting, sell
a painting, print a report, update a fashionability
coefficient, or quit

These possibilities are indicated by the five events:
–
–
–
–
–
buy painting selected
sell painting selected
print report selected
update fashionability selected
quit selected
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Initial Dynamic Model: Osbert Oglesby

Slide 6B.10
The initial main menu in the target Osbert Oglesby
information system
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Initial Dynamic Model: Osbert Oglesby (contd)
Slide 6B.11

Suppose that Osbert clicks on Buy a painting in the
menu
– The event buy painting selected has now occurred
– The system moves from its current state, Osbert Oglesby
Information System Loop, to the state Buying a
Painting

In Buying a Painting state, Osbert can
– Buy a masterpiece, masterwork, or other painting
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Initial Dynamic Model: Osbert Oglesby (contd)
Slide 6B.12

The Osbert Oglesby information system moves from
state to state when an event occurs
– In each state, Osbert performs one of the operations
supported by that state

This continues until Osbert clicks on option Quit
while the system is in state Oglesby Information
System Loop
– At this time the information system enters the final state
(represented by the white circle containing the small black
circle)
– This terminates execution of the statechart
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Dynamic Modeling (contd)

Slide 6B.13
Traditionally there is a dynamic model for each
class, rather than for the system as a whole, as in
this case study
– However, objects in information systems rarely move from
one class to another class

Accordingly, a dynamic model for the information
system as a whole is appropriate
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Extracting Boundary Classes

Slide 6B.14
It is usually easy to extract boundary classes
– Each input screen, output screen, and printed report is
generally modeled by a boundary class
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Initial Boundary Classes: Osbert Oglesby
Slide 6B.15

One screen should be adequate for all four Osbert
Oglesby use cases:
–
–
–
–

Buy a Painting
Sell a Painting
Print a Report
Modify a Fashionability Coefficient
Thus there is one initial boundary class
– User Interface Class
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Initial Boundary Classes: Osbert Oglesby (contd)
Slide 6B.16

Consider again the first iteration of the main menu of
the user-interface screen

The five commands correspond precisely to the five
events in the statechart
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Initial Boundary Classes: Osbert Oglesby (contd)
Slide 6B.17

This is a graphical interface, which needs special
software
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Initial Boundary Classes: Osbert Oglesby (contd)
Slide 6B.18

However, a textual interface runs on all computers
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Initial Boundary Classes: Osbert Oglesby (contd)
Slide 6B.19

There are three reports:
– The purchases report
– The sales report
– The future trends report

Each of these has to be modeled by a separate
boundary class because the content of each report
is different
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Initial Boundary Classes: Osbert Oglesby (contd)
Slide 6B.20

There are thus three report boundary classes
– Purchases Report Class
– Sales Report Class
– Future Trends Report Class
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Initial Boundary Classes: Osbert Oglesby (contd)
Slide 6B.21

There are therefore four boundary classes
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Extracting Control Classes

Slide 6B.22
It is also usually easy to extract control classes
– Each nontrivial computation is generally modeled by a
control class
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Initial Control Classes: Osbert Oglesby

Slide 6B.23
In the case study there are four computations
– Determining the maximum price that Osbert should offer
for a
» Masterpiece
» Masterwork, or
» Other painting
– Determining if there is a new trend in art purchases
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Initial Control Classes: Osbert Oglesby

There are thus four initial control classes:
–
–
–
–
Compute Masterpiece Price Class
Compute Masterwork Price Class
Compute Other Painting Price Class
Compute Future Trends Class
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Slide 6B.24
Initial Control Classes: Osbert Oglesby (contd)
Slide 6B.25

Here are the initial control classes
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Refining the Use Cases: Osbert Oglesby
Slide 6B.26

The class diagram reflects that the pricing algorithm
treats the three types of paintings differently

Accordingly, use case Buy a Painting needs to be
refined into three separate use cases
– Buy a Masterpiece
– Buy a Masterwork
– Buy Other Painting

Therefore, the description of the Buy a Painting use
case must be split into three separate descriptions
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Refining the Use Cases: Osbert Oglesby (contd)
Slide 6B.27

The Produce a Report use case also needs to be
refined
– The purchases report and the sales report use simple data
extraction— the future trends report involves computation
– All three reports use their own boundary classes
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Refining the Use Cases: Osbert Oglesby (contd)
Slide 6B.28

For both these reasons, the Produce a Report use
case must be refined into three use cases
– Produce a Purchases Report
– Produce a Sales Report
– Produce a Future Trends Report

The description of the use case must be split into
three separate descriptions
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Third Iteration of the Use-Case Diagram
Slide 6B.29
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Class Extraction (contd)

The description of class extraction is complete

We now therefore return to the Unified Process
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Slide 6B.30
Use-Case Realization

Slide 6B.31
The process of extending and refining use cases is
called use-case realization
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Use-Case Realization (contd)

Slide 6B.32
The verb “realize” is used at least 3 different ways:
– Understand (“Harvey slowly began to realize that he was
in the wrong classroom”);
– Receive (“Ingrid will realize a profit of $45,000 on the
stock transaction”); and
– Accomplish (“Janet hopes to realize her dream of starting
a computer company”)

In the phrase “realize a use case,” the word “realize”
is used in this last sense
– It means to accomplish (or achieve) the use case
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Use-Case Realization (contd)

Slide 6B.33
The realization of a specific scenario of a use case
is depicted using an interaction diagram
– Either a sequence diagram or collaboration diagram

Various versions of the use case Buy a Masterpiece
appear in the following slides
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Buy a Masterpiece Use Case

Use case diagram
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Slide 6B.34
Buy a Masterpiece Use Case (contd)

Description
of the use
case
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Slide 6B.35
Buy a Masterpiece Use Case (contd)

Slide 6B.36
Class diagram (classes that enter into the use case)
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Buy a Masterpiece Use Case (contd)

Slide 6B.37
The four classes that enter into this use case are:
– User Interface Class
» This class models the user interface
– Compute Masterpiece Price Class
» This class models the computation of the price Osbert should offer
– Masterpiece Class
» The computation involves comparing the masterpiece being
considered with the masterpieces that have been previously
auctioned
– Auctioned Painting Class
» These masterpieces are all instances of Auctioned Painting
Class
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Buy a Masterpiece Use Case (contd)

Slide 6B.38
The Seller does not interact directly with the
information system
– Instead, the Seller provides data that Osbert enters into
the information system

This is indicated in the note (the rectangle with the
top right-hand corner turned over)
– There is a dashed line from the note to the item to which it
refers, the Seller in this case
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Buy a Masterpiece Use Case (contd)

Slide 6B.39
Scenario (one possible instance of the use case)
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Buy a Masterpiece Use Case (contd)

Slide 6B.40
A working information system uses objects, not
classes
– Example: A specific masterpiece is not represented by
Masterpiece Class but rather by an object, a specific
instance of Masterpiece Class

Such an object is denoted by : Masterpiece Class
Copyright © 2004 by The McGraw-Hill Companies, Inc. All rights reserved.
Buy a Masterpiece Use Case (contd)

A class diagram shows the classes in the use case
and their relationships
– It does not show the objects nor the sequence of
messages as they are sent from object to object

Slide 6B.41
Something more is needed
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Buy a Masterpiece Use Case (contd)

Collaboration diagram (of the realization of the
scenario of the use case)
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Slide 6B.42
Buy a Masterpiece Use Case (contd)
Slide 6B.43

The collaboration diagram shows the objects as well
as the messages, numbered in the order in which
they are sent in the specific scenario

The direction of the arrow shows the direction in
which the information flows
Copyright © 2004 by The McGraw-Hill Companies, Inc. All rights reserved.
Slide 6B.44
Continued in Unit 6C
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