Chapter 7

Report
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Chapter 7:
The Object-Oriented Approach
to Requirements
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World, 3rd Edition
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Learning Objectives
 Develop
 Write
use case diagrams
use case and scenario descriptions
 Develop
activity diagrams and system sequence
diagrams
 Refine
and enhance the domain model class
diagram
 Explain
how UML diagrams work together to
define functional requirements for the objectoriented approach
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Overview
 Objective
of requirements definition is
understanding user’s needs, business processes,
and system to support business processes
 Understand
and define requirements for a new
system using object-oriented analysis models
and techniques
 Line
between object-oriented analysis and objectoriented design is somewhat fuzzy

Iterative approach to development

Models built in analysis are refined during design
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The Unified Modeling Language and the
Object Management Group
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 Object-oriented
modeling notation is Unified
Modeling Language (UML)
 UML
was presented to Object Management
Group (OMG) as standard modeling technique
 Purpose
of Object Management Group

Promote theory and practice of object technology
for development of distributed systems

Provide common architectural framework for OO
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Object-Oriented Requirements
 Object-oriented
system requirements are
specified and documented through process of
building models
 Systems
development process starts with
identification of events and things
 Events
are business processes that new system
must address
 Things
are problem domain objects involved in
business process
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Object-Oriented Approach Models
 Class
diagram – definition of system components
case diagrams and use case descriptions –
show user roles and how they use the system
 Use
sequence diagrams (SSDs) – define
inputs and outputs and sequence of interactions
between user and system for a use case
 Systems
 Statechart
diagrams – describe states of each
object
 Activity
diagrams – describe user activities
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Requirements Diagrams: Traditional and
OO Models
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The System Activities –
A Use Case / Scenario View
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 Use
case analysis used to identify and define all
business processes that system must support
 Use
Case - single function performed by system
for those who use that function
 Actors

Role played by user

Outside automation boundary and organization
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Use Case Diagram
 Graphical
models that summarize information
about actors and use cases
 System
developer

Looks at system as whole

Identifies major uses from event table

Identifies functions to be supported by new system

Organizes use cases
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Simple Use Case with an Actor
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Use Case Diagram with System Boundary
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Use Case of Customer Support System
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All Use Cases Including Customer
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<<Includes>> Relationships
 Documents
situation where one use case
requires the services of a common subroutine
 Another
use case is developed for this common
subroutine
 A common
use case can be reused by multiple
use cases
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Example of Order-Entry Subsystem with
<<Includes>> Use Cases
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Developing a Use Case Diagram
 Starting
points for use case development

Use event table

Identify all actors of the system

Identify functions actors perform with system
 Develop
flow of activities to identify various
scenarios
 Common
internal use cases can be identified and
separated into different use cases
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CRUD analysis
 CRUD
– Create, Read/Report, Update, Delete
 Information
Engineering (IE) technique to identify
event table events or develop use case diagram
 Compares
identified use cases with domain
model class diagram
 Every
class in class diagram must have use
cases to support creating, reading, reporting,
updating, and deleting object instances
 Confirms
system integration requirements
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Use Case Detailed Descriptions
 Scenario,
or use case instance, details sequence
of activities within use case
 Shows
actor interacting with computer system
step-by-step to carry out business activity
 May
have several scenarios for single use case
 Analysts
prefer to write narrative descriptions of
use cases instead of building activity diagrams
 Three
levels: brief, intermediate, and fully
developed description
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Brief Description of Create New Order
Use Case
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Intermediate Description of the Telephone
Order Scenario for Create New Order
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Intermediate Description of the Web
Order Scenario for Create New Order
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Fully Developed Description of Telephone
Order Scenario for Create New Order
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Fully Developed Description of Web
Order Scenario for Create New Order
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Activity Diagrams
 Used
to document work flow of business process
activities for each use case scenario
 Standard
 Can
UML diagram
support any level of use case description
 Helpful
in developing system sequence diagrams
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Activity Diagram: Telephone Order Scenario
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Activity Diagram: Web Order Scenario
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Identifying Inputs and Outputs –
The System Sequence Diagram
 Collaboration
diagram

Emphasizes objects that interact together to
support a use case diagram

May be used alone or with sequence diagram
 System
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sequence diagram

Shows sequence of interactions between objects
and flow of events in a single use case

Focuses on message details

Used more frequently in industry
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Sample System Sequence Diagram (SSD)
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SSD Notation
represented by stick figure – person (or
role) that “interacts” with system by entering input
data and receiving output data
 Actor
 Object
notation is rectangle with name of object
underlined – shows individual object and not
class of all similar objects
 Lifeline
is vertical line under object or actor to
show passage of time for object
 Messages
use arrows to show messages sent or
received by actor or system
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SSD Lifelines
 Vertical

 If
line under object or actor:
Shows passage of time
vertical line dashed:

Creation and destruction of thing is not important
for scenario
 Long

narrow rectangles:
Activation lifelines emphasize that object is active
only during part of scenario
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SSD Messages
 Internal
events identified by the flow of objects
within a scenario
 Requests
from one actor or object to another to
do some action
 Invokes
a particular method
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Repeating Message
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Developing a System Sequence Diagram
 Begin
with detailed description of use case from
fully developed form or activity diagrams
 Identify
input messages
 Describe
message from external actor to system
using message notation
 Identify
and add any special conditions on input
message, including iteration and true/false
conditions
 Identify
and add output return messages
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Simplified Activity Diagram of the
Telephone Order Scenario
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SSD of Simplified Telephone Order
Scenario for Create New Order Use Case
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SSD of the Web Order Scenario for the
Create New Order Use Case
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Problem Domain Modeling –
The Domain Model Class Diagram
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 Class
diagram is focal point of object-oriented
development
 Provides
definition of system components
 Contains
important class structural information for
implementation with object-oriented programming
 Provides
conceptual data model to describe
classes for database definition
 Consists
of problem domain classes and
implementation classes
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Example of Domain Model Class Diagram
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RMO Domain Model Class Diagram
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Integrating Object-Oriented Models
 Complete
use case diagram is needed to
understand total scope of new system
 Domain
model class diagrams also should be as
complete as possible for entire system
 With
iterative approach, only construct use case
descriptions, activity diagrams, and system
sequence diagrams for use cases in iteration
 Development
of a new diagram often helps refine
and correct previous diagrams
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Relationships Between OO
Requirements Models
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Use Case Diagram for Inventory System
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Summary
 Object-oriented
approach has complete set of
diagrams that together document the user’s need
and define system requirements
 Requirements
specified using following models:

Domain model class diagrams

Use case diagrams

Use case detailed model, either descriptive format
or activity diagram

System sequence diagrams (SSDs)
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