Transcript Lecture for Chapter 4, Requirements Elicitation

Using UML, Patterns, and Java
Object-Oriented Software Engineering
Requirements Elicitation
Where are we right now?

Three ways to deal with complexity:
 Abstraction
 Decomposition (Technique: Divide and conquer)
 Hierarchy (Technique: Layering)
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Two ways to deal with decomposition:
 Object-orientation and functional decomposition
 Functional decomposition leads to unmaintainable code
 Depending on the purpose of the system, different objects can be
found

What is the right way?
 Start with a description of the functionality (Use case model). Then
proceed by finding objects (object model).

What activities and models are needed?
 This leads us to the software lifecycle we use in this class
Modified from originals of Bruegge &. Dutoit
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Software Lifecycle Definition
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Software lifecycle:
 Set of activities and their relationships to each other to support the
development of a software system
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Typical Lifecycle questions:
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Which activities should I select for the software project?
What are the dependencies between activities?
How should I schedule the activities?
What is the result of an activity
Modified from originals of Bruegge &. Dutoit
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Software Lifecycle Activities
Requirements Requirements System
Elicitation
Design
Analysis
Expressed in
Terms Of
Structured By
Object
Design
Implementation
Implemented
By
Realized By
Verified
By
class...
class...
class...
Use Case
Model
Modified from originals of Bruegge &. Dutoit
Application
SubSystems
Domain
Objects
Testing
Solution
Domain
Objects
Source
Code
Object-Oriented Software Engineering: Using UML, Patterns, and Java
?
class.... ?
Test
Cases
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First Step in Establishing the Requirements:
System Identification
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The development of a system is not just done by taking a
snapshot of a scene (domain)
Two questions need to be answered:
 How can we identify the purpose of a system?
 Crucial is the definition of the system boundary: What is inside,
what is outside the system?
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These two questions are answered in the requirements process
The requirements process consists of two activities:
 Requirements Elicitation:
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Definition of the system in terms understood by the customer
(“Problem Description”)
 Requirements Analysis:

Technical specification of the system in terms understood by the
developer (“Problem Specification”)
Modified from originals of Bruegge &. Dutoit
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Products of Requirements Process
Problem
Statement
Requirements
Elicitation
(Activity Diagram)
Problem
Statement
Generation
system
specification:
Model
Requirements
Analysis
analysis
model: Model
Modified from originals of Bruegge &. Dutoit
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System Specification vs Analysis Model
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Both models focus on the requirements from the user’s view of
the system.
System specification uses use cases and natural language to
describe the behavior
The analysis model uses formal or semi-formal notation
They are both part of the Requirements Analysis Document
Modified from originals of Bruegge &. Dutoit
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Requirements Analysis Document
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Introduction
Current System
Proposed System
 Functional requirements
 Nonfunctional requirements
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System Models
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Scenarios
Use case model
Object model
Dynamic model
User interface
Glossary
Modified from originals of Bruegge &. Dutoit
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Requirements Elicitation
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Overview and Challenges
Problem Statement
Functional and Nonfunctional Requirements
Requirements Validation Criteria
Modified from originals of Bruegge &. Dutoit
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Requirements Elicitation

Very challenging activity
 Users don’t know what they need the system to do. They could not
articulate their needs.
 Users don’t understand the limits of the available technology.
 Users express requirements using terms from their application
domain.
 Users representing different stakeholders have requirements that
vary to some degree.
 Political factors may influence how users express requirements.
 The economic and business environment is constantly changing and
can affect the relative importance of certain requirements.
Modified from originals of Bruegge &. Dutoit
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Requirements Elicitation

Requires collaboration of people with different backgrounds
 Users with application domain knowledge
 Developer with solution domain knowledge (design knowledge,
implementation knowledge)
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Bridging the gap between user and developer:
 Scenarios: Example of the use of the system in terms of a series of
interactions with between the user and the system
 Use cases: Abstraction that describes a class of scenarios
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Starts with Problem Statement
Modified from originals of Bruegge &. Dutoit
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Problem Statement
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The problem statement is developed by the client as a
description of the problem addressed by the system
Other terms for problem statement:
 Statement of Work
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A good problem statement describes
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The current situation
The functionality the new system should support
The environment in which the system will be deployed
Deliverables expected by the client
Delivery dates
A set of acceptance criteria
Modified from originals of Bruegge &. Dutoit
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Ingredients of a Problem Statement
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Current situation: The Problem to be solved
Description of one or more scenarios
Requirements
 Functional and Nonfunctional requirements
 Constraints (“pseudo requirements”)
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Project Schedule
 Major milestones that involve interaction with the client including deadline
for delivery of the system
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Target environment
 The environment in which the delivered system has to perform a specified
set of system tests
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Client Acceptance Criteria
 Criteria for the system tests
Modified from originals of Bruegge &. Dutoit
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Categories of Projects
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Current situation depends on the category of the project
Greenfield Engineering
 No prior system exists or existing system is being significantly extended
with new functionality
 The requirements are extracted from the end users and the client
 Triggered by new user needs
 Example: A new online boardgame
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Re-engineering
 Re-design and/or re-implementation of an existing system using newer
technology, essential purpose of system is unchanged
 The requirements are reverse engineered from the existing system
 Triggered by technology enabler
 Example: Replacing a mainframe COBOL system with SAP
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Interface Engineering
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Provide the services of an existing system in a new environment
Requirements are dictated by users and existing system behavior
Triggered by technology enabler or new market needs
Example: Replacing curses-based forms with web-based forms
Modified from originals of Bruegge &. Dutoit
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Types of Requirements
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Functional requirements:
 Describe the interactions between the system and its environment
independent from implementation
 Examples:
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The system should alert the dispatcher of a new incident.
Nonfunctional requirements:
 User visible aspects of the system not directly related to functional
behavior.
 Examples:
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The response time must be less than 1 second within the reporting of the
incident.
Constraints (“Pseudo requirements”):
 Imposed by the client or the environment in which the system operates
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The implementation language must be Java
Modified from originals of Bruegge &. Dutoit
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Requirements Validation
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Activity involving the client and user
Requirements validation is a critical step in the development
process, usually after requirements engineering or requirements
analysis. Also at delivery (client acceptance test).
Modified from originals of Bruegge &. Dutoit
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Requirements Validation Criteria
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Completeness
 All possible scenarios through the system are described, including exceptions
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Consistency
 There are no contradicting requirements
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Clarity/Unambiguity
 The specification can only be interpreted one way
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Correctness
 Requirements represent accurately the system the client needs
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Realism
 The system can be implemented within constraints
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Verifiability
 Tests can be designed to demonstrate the system fulfills its requirements
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Traceability
 Requirements can be traced to system functions
 System functions can be traced to requirements
 Dependencies among requirements, system functions, and everything else in between
can be tracked.
Modified from originals of Bruegge &. Dutoit
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Requirements Elicitation Activities
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Identifying Actors
Identifying Scenarios
Identifying Use Cases
Refining Use Cases
Identifying Relationships between Actors and Use Cases
Identifying Initial Analysis Objects
Identifying Nonfunctional Requirements
Modified from originals of Bruegge &. Dutoit
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Identifying Actors
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Actors – person or machine using the system in a particular role
Actors usually correspond to existing roles within the client
organization
Guide Questions
 Which user groups are supported by the system to perform their
work?
 Which user groups execute the system’s main functions?
 Which user groups perform secondary functions, such as
maintenance and administration?
 With what external hardware or software system will the system
interact?

Watch out for confusion between actors and objects
Modified from originals of Bruegge &. Dutoit
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Identifying Scenarios
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Scenario
 “A narrative description of what people do and experience as they
try to make use of computer systems and applications” [Carrol,
Scenario-based Design, 1995]
 Informal description of a single feature from the viewpoint of a
single actor

Types of Scenarios
 As-is scenarios – describes current situation
 Visionary scenarios – describes future system
 Evaluation scenarios – describes user tasks for evaluating the
system (acceptance criteria)
 Training scenarios – introduces new users to the system
Modified from originals of Bruegge &. Dutoit
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Heuristics for Identifying Scenarios

Ask yourself or the client the following questions:
 What are the primary tasks that the system needs to perform?
 What data will the actor create, store, change, remove or add in the
system? Who else can modify this data?
 What external changes does the system need to know about?
 What changes or events will the actor of the system need to be
informed about?
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However, don’t rely on questionnaires alone.
Insist on task observation if the system already exists (interface
engineering or reengineering)
 Ask to speak to the end user, not just to the software contractor
 Expect resistance and try to overcome it
Modified from originals of Bruegge &. Dutoit
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Scenario Example: Warehouse on Fire

Bob, driving down main street in his patrol car notices smoke coming out of
a warehouse. His partner, Alice, reports the emergency from her car.
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Alice enters the address of the building, a brief description of its location
(i.e., north west corner), and an emergency level. In addition to a fire unit,
she requests several paramedic units on the scene given that area appear to
be relatively busy. She confirms her input and waits for an acknowledgment.

John, the Dispatcher, is alerted to the emergency by a beep of his
workstation. He reviews the information submitted by Alice and
acknowledges the report. He allocates a fire unit and two paramedic units to
the Incident site and sends their estimated arrival time (ETA) to Alice.

Alice received the acknowledgment and the ETA.
Modified from originals of Bruegge &. Dutoit
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Observations about Warehouse on Fire Scenario
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Concrete scenario
 Describes a single instance of reporting a fire incident.
 Does not describe all possible situations in which a fire
can be reported.
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Participating actors
 Bob, Alice and John
Modified from originals of Bruegge &. Dutoit
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Another Example
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Bob takes server out of service for software upgrades
System detects that server is no longer active
System identifies backup server
manage.ist.unomaha.edu is notified to switch to IP address of
backup server
manage.ist.unomaha.edu replaces IP address in its lookup table
Modified from originals of Bruegge &. Dutoit
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Identifying Use Cases
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Use Case
 Specifies all possible scenarios for a given functionality
 Initiated by an actor
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Motivations for use cases
 Generalizing related scenarios help developers define the scope of
the system
 The role of each user of the system is clarified
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Use Case Descriptions
 Entry and exit conditions
 Flow of events
 Quality requirements
Modified from originals of Bruegge &. Dutoit
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Heuristics: How do I find use cases?
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Select a narrow vertical slice of the system (i.e. one scenario)
 Discuss it in detail with the user to understand the user’s preferred
style of interaction
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Select a horizontal slice (i.e. many scenarios) to define the
scope of the system.
 Discuss the scope with the user
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Use illustrative prototypes (mock-ups) as visual support
Find out what the user does
 Task observation (Good)
 Questionnaires (Bad)
Modified from originals of Bruegge &. Dutoit
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Order of steps when formulating use cases
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First step: name the use case
 Use case name: ReportEmergency

Second step: Find the actors
 Generalize the concrete names (“Bob”) to participating actors
(“Field officer”)
 Participating Actors:
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
Field Officer (Bob and Alice in the Scenario)
Dispatcher (John in the Scenario)
Third step: Then concentrate on the flow of events
 Use informal natural language
Modified from originals of Bruegge &. Dutoit
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Use Case Example: ReportEmergency
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Use case name: ReportEmergency
Participating Actors:
 Field Officer (Bob and Alice in the Scenario)
 Dispatcher (John in the Scenario)

Exceptions:
 The FieldOfficer is notified immediately if the connection between
her terminal and the central is lost.
 The Dispatcher is notified immediately if the connection between
any logged in FieldOfficer and the central is lost.

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Flow of Events: on next slide.
Special Requirements:
 The FieldOfficer’s report is acknowledged within 30 seconds. The
selected response arrives no later than 30 seconds after it is sent by
the Dispatcher.
Modified from originals of Bruegge &. Dutoit
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Use Case Example: ReportEmergency
Flow of Events
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The FieldOfficer activates the “Report Emergency” function of her
terminal. FRIEND responds by presenting a form to the officer.

The FieldOfficer fills the form, by selecting the emergency level, type,
location, and brief description of the situation. The FieldOfficer also
describes possible responses to the emergency situation. Once the form is
completed, the FieldOfficer submits the form, at which point, the
Dispatcher is notified.

The Dispatcher reviews the submitted information and creates an Incident in
the database by invoking the OpenIncident use case. The Dispatcher selects
a response and acknowledges the emergency report.

The FieldOfficer receives the acknowledgment and the selected response.
Modified from originals of Bruegge &. Dutoit
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Identifying Use Cases
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Writing Guide
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Choose proper name – use verb phrases; indicate user’s objective
Name actors with noun phrases
Clearly distinguish actors’ actions from system’s actions
Use active voice to phrase steps in flow of events
The causal relationship between steps should be clear
Describe complete user transaction
Describe exceptions separately
Do not describe the user interface
Use cases should not exceed 2-3 pages – break up using <<include>>
and <<extends>> relationships
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Refining Use Cases
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Goal: completeness and correctness
Refining use case descriptions leads to other use cases and
clarifies system boundaries
 Entry and exit conditions – additional use cases are identified as
entry and exit conditions are refined
 Flow of events – discussing flow of events clarifies system
boundaries
 Quality requirements – elicit nonfunctional requirements in the
context of this particular functionality
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Refinements
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Details of objects in the system
Low-level interactions between actors and system
Access rights
Missing exceptions
Common functionality among use cases
Modified from originals of Bruegge &. Dutoit
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Refining Use Cases
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Heuristics
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Use scenarios to communicate with users and validate functionality
Refine a single scenario to understand user’s assumptions
Define many high-level scenarios to determine scope of the system
Use mock-ups or prototypes for visual support
Present user with a range of alternatives
Detail a broad vertical slice when scope of system and user
preferences are well-understood
Modified from originals of Bruegge &. Dutoit
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Relationships Between Actors and Use Cases
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Relationships between actors and use cases
 <<initiate>>
 <<participate>>
 Determines access rights
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Who can initiate a functionality
Who else is involved in this functionality
Relationships between use cases
 Heuristics for making use cases shorter and simpler to understand
 <<include>>
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For factoring out common functionality
Explicitly invoked from the including use case
 <<extend>>
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For specifying exceptions
Entry conditions of the extending use case determine when it is used
 Caveat: use discretion when applying these decompositions (a few longer
use cases are sometimes easier to understand than many short ones)
Modified from originals of Bruegge &. Dutoit
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<<Include>>: Functional Decomposition
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Problem:
 A function in the original problem statement is too complex to be
solvable immediately
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Solution:
 Describe the function as the aggregation of a set of simpler
functions. The associated use case is decomposed into smaller use
cases
ManageIncident
<<include>>
CreateIncident
Modified from originals of Bruegge &. Dutoit
HandleIncident
CloseIncident
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<<Include>>: Reuse of Existing Functionality
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Problem:
 There are already existing functions. How can we reuse them?
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Solution:
 The include association from a use case A to a use case B indicates
that an instance of the use case A performs all the behavior
described in the use case B (“A delegates to B”)
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Example:
 The use case “ViewMap” describes behavior that can be used by
the use case “OpenIncident” (“ViewMap” is factored out)
<<include>>
OpenIncident
Base Use
Case
ViewMap
<<include>>
AllocateResources
Supplier
Use Case
Note: The base case cannot exist alone. It is always called with the
supplier use case
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<Extend>> Association for Use Cases
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Problem:
 The functionality in the original problem statement needs to be
extended.
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Solution:
 An extend association from a use case A to a use case B indicates that use
case B is an extension of use case A.

Example:
 The use case “ReportEmergency” is complete by itself , but can be
extended by the use case “ConnectionDown” for a specific scenario in
which the user cannot communicate with the dispatcher
ConnectionDown
FieldOfficer
f
<<extend>>
ReportEmergency
Note: The base use case can be executed without the use case extension
in extend associations.
Modified from originals of Bruegge &. Dutoit
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Identifying Initial Analysis Objects
Level 1
Level 2
Level 3
Modified from originals of Bruegge &. Dutoit
Level 2 Use Cases
Level 2
Level 3
Level 3
Level 4
A
Top Level Use Case
Level 3 Use Cases
Operations
Level 4
B
Object-Oriented Software Engineering: Using UML, Patterns, and Java
A and B
are called
Participating
Objects
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Use Cases can be used by more than one object
Level 1
Level 2
Level 3
Level 2 Use Cases
Level 2
Level 3
Level 3
Level 4
A
Top Level Use Case
Level 3 Use Cases
Operations
Level 4
B
Participating
Objects
Modified from originals of Bruegge &. Dutoit
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Identifying Initial Analysis Objects
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Identify the participating objects to create the initial analysis object model
Maintaining glossary of objects minimizes potential confusion in
terminology between users and developers
Heuristics
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Terms the needed clarification (by developer or user)
Recurring nouns in use cases
Real-world entities and resources that system must track
Use cases
Data sources or sinks
Artifacts with which user interacts
Use application domain terms
Cross-check
 Eliminate ambiguity: verify that objects with the same name refer to the
same concept
 Maintain consistency: verify that objects do not refer to the same concept
using different names
 Eliminate objects not involved in any use cases
Modified from originals of Bruegge &. Dutoit
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Identifying Nonfunctional Requirements
(FURPS+ Classification Scheme)
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Quality Requirements
 Usability
 Reliability/Dependability
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Safety
Security
Survivability
 Performance
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Pseudo Requirements
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Implementation
Interface
Operations
Packaging
Legal
Response Time
Throughput
Availability
Accuracy
 Supportability
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Adaptability
Maintainability
Portability
Modified from originals of Bruegge &. Dutoit
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Identifying Nonfunctional Requirements
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Heuristics
 Use a taxonomy (e.g., FURPS+) to generate checklists
 Give different checklists to users in appropriate roles
 Checklists vary depending on application domain
Modified from originals of Bruegge &. Dutoit
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How to Specify a Use Case (Summary)
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Name of Use Case
Actors
 Description of Actors involved in use case)
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Entry condition
 “This use case starts when…”
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Flow of Events
 Free form, informal natural language
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Exit condition
 “This use cases terminates when…”
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Exceptions
 Describe what happens if things go wrong

Special Requirements
 Nonfunctional Requirements, Constraints)
Modified from originals of Bruegge &. Dutoit
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Managing Requirements Elicitation
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Negotiating specifications
Maintaining traceability
Tool support
Modified from originals of Bruegge &. Dutoit
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Negotiating Specifications (JAD)
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Use case modeling is useful in requirements elicitation, but it is
not the only activity
Requirements have to be identified and negotiated between
different stakeholders
JAD – Joint Application Design
A moderated meeting with all stakeholders participating
 Users, clients, developers + trained facilitator
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Leverages group dynamics of face-to-face meetings
Developers get to understand application domain
Users get to understand potential solution domain tradeoffs
Modified from originals of Bruegge &. Dutoit
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JAD Activities
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Project definition
 Facilitator determines objectives and scope of project through
interviews with project manager and client
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Research
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Facilitator interviews present and future users
Facilitator gathers information about application domain
Facilitator creates initial high-level use cases
Facilitator creates initial list of problems
Preparation
 Facilitator creates Working Document, agenda and presentation
materials
 Facilitator forms team with adequate representation from all
stakeholders
Modified from originals of Bruegge &. Dutoit
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JAD Activities
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Session
 Facilitator guides team in creating the requirements specification
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Discover new requirements
Classify and organize requirements
Prioritize requirements
Validate requirements
Derive use cases
Activities are repeated until closure is achieved
Final document preparation
 Facilitator prepares Final Document
 Team reviews and approves Final Document
Modified from originals of Bruegge &. Dutoit
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JAD Facilitator
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Qualifications of JAD facilitator is crucial
Must keep the discussion within the scope of the project
Discern wants from needs
Keep the discussion within the application domain to avoid
prescribing requirements that restrict the solution space
unnecessarily (pushing specific technology, methodology or
language)
Mediate disputes before they get out of hand
Watch out for political influences and hidden agendas
Modified from originals of Bruegge &. Dutoit
Object-Oriented Software Engineering: Using UML, Patterns, and Java
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Maintaining Traceability
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Traceability the ability to follow the life of a requirement as it
is translated into design and then implementation and test cases
The system is complete when all requirements can be traced to
implementation
Traceability also enables developers to uncover the rationale
behand certain requirements and design decisions
Traceability is harder for nonfunctional requirements
Traceability is difficult to maintain manually
 Need to maintain cross-references between different artifacts
(requirements, design documents, code, test plan, user
documentation)
 Need tool support
Modified from originals of Bruegge &. Dutoit
Object-Oriented Software Engineering: Using UML, Patterns, and Java
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Tool Support
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Requirements for Managing Requirements
 Store requirements in a shared repository
 Provide multi-user access
 Automatically create a system specification document from the
repository
 Allow change management
 Provide traceability throughout the project lifecycle
Modified from originals of Bruegge &. Dutoit
Object-Oriented Software Engineering: Using UML, Patterns, and Java
51
Summary
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The requirements process consists of requirements elicitation and analysis.
The requirements elicitation activity is different for:
 Greenfield Engineering, Reengineering, Interface Engineering
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Scenarios:
 Great way to establish communication with client
 Different types of scenarios: As-Is, visionary, evaluation and training
 Use cases: Abstraction of scenarios
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Pure functional decomposition is bad:
 Leads to unmaintainable code
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Pure object identification is bad:
 May lead to wrong objects, wrong attributes, wrong methods
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The key to successful analysis:
 Start with use cases and then find the participating objects
 If somebody asks “What is this?”, do not answer right away. Return the
question or observe the end user: “What is it used for?”
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Use case modeling is a part of the requirements elicitation process, not the
entire process itself.
Modified from originals of Bruegge &. Dutoit
Object-Oriented Software Engineering: Using UML, Patterns, and Java
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