Last Lectures
♦ Use Case Model
 Detailled use case - Important
 Use case diagram- Refactoring Use case
diagram
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
<<Include>>
<<Extend>>
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Last Lectures
♦ DOMAIN Model
• Conceptual classes ( object , events , idea …etc)
• Attributes
 Data value of an object.
 To remember information
• Associations
 Relationship between conceptual classes
• Multiplicities
 many instances can be validly associated with another
instance
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What we did !!!
Sample UP Artifact Relationships
Domain Model
Sale
Business
Modeling
Sales
LineItem
1..*
1
date
. . .
. . .
. . .
quantity
Vision
Use-Case Model
Process Sale
Process
Sale
use
case
names
Cashier
Requirements
Use Case Diagram
1. Customer
arrives ...
2. Cashier
makes new
sale.
3. ...
parameters and
return value details
Use Case Text
Glossary
system
events
: System
Operation:
enterItem(…)
Post-conditions:
- . . .
: Cashier
system
operations
make
NewSale()
Supplementary
Specification
enterItem
(id, quantity)
System Sequence Diagrams
Operation Contracts
starting events to design for
: Register
Design
Design Model
: ProductCatalog
enterItem
(itemID, quantity)
spec = getProductSpec( itemID )
addLineItem( spec, quantity )
: Sale
System Sequence
Diagrams
Chapter 10
Applying UML and Patterns
-Craig Larman
Introduction

Class diagrams represent static
modeling.

What about modeling dynamic behavior?
Interaction diagrams (Sequence and
communication diagrams) model how
groups of object collaborate to perform some
behavior
Typically captures the behavior of a single

use case
Today´s
lecture
System Sequence Diagram (SSD)
For a use case scenario, an SSD shows:
 The System (as a black box) :System
 The external actors that interact with System
 The System events that the actors generate ,
their temporal order.
How to construct an SSD from a
use case
System Sequence Diagrams
♦ Draw a line representing the system as a
black box.
♦ Identify each actor that directly operates on
the system. Draw a line for each such actor.
♦ From detailled (expanded) use case identify system
events that each actor generates. Illustrate them
♦ Optionally include use case text on left.
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Relationship SSD and Use case
Develop SSDs for the main success scenario of a selected use
case, then frequent alternative scenarios
Process Sale
system as black box
the name could be "NextGenPOS" but "System" keeps it
simple
the ":" and underline imply an instance, and are explained in a
later chapter on sequence diagram notation in the UML
external actor to
system
Process Sale Scenario
:System
: Cashier
makeNewSale
a UML loop
interaction
frame, with a
boolean guard
expression
loop
[ more items ]
enterItem(itemID, quantity)
description, total
endSale
return value(s)
associated with the
previous message
an abstraction that
ignores presentation
and medium
the return line is
optional if nothing is
returned
total with taxes
makePayment(amount)
change due, receipt
a message with
parameters
it is an abstraction
representing the
system event of
entering the
payment data by
some mechanism
Relationship between SSD and
Use case
Naming System events & operations

System events and associated system operations
should be expressed at the level of intent.

Rather than physical input medium or UI widget

Start operation names with verb (from use case)

Which is better, scanBarCode or enterItem?
Naming System events & operations
Capture the intent of
the operation while
remaining abstract
:System
: Cashier
better name
enterItem(itemID, quantity)
scan(itemID, quantity)
worse name
SSDs and the Glossary in parallel
Why is updating the glossary important
when developing the SSD?
 New terms used in SSDs may need
explanation, especially if they are not
derived from use cases
 A glossary is less formal, easier to
maintain and more intuitive to discuss
with external parties such as customers
Why Draw SSD?




Actually , we investigate the behaviour of
the system as black box (what system do).
It is Important to know events that are
coming in our system
Later during design , the software is
designed to handle these events
In design , we will open the black box and
look on how object collaborate to achieve
what should be done
Example 1
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Example 2
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Question please!!
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