Requirements Elicitation

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Requirements Elicitation
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Where are we right now?

• Three ways to deal with complexity
• Abstraction
• Decomposition (Technique Divide and conquer)
• Hierarchy (Technique Layering)
• 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

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Software Lifecycle Definition

• Software lifecycle
• Set of activities and their relationships to each
  other to support the development of a software
  system
• Typical Lifecycle questions
• 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

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Software Lifecycle Activities
System Design
Object Design
Implemen- tation
Testing
Requirements Elicitation
Requirements Analysis
Implemented By
Expressed in Terms Of
Structured By
Realized By
Verified By
?
?
Application Domain Objects
Solution Domain Objects
Use Case Model
Source Code
SubSystems
Test Cases
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First Step in Establishing the Requirements
System Identification

• 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?
• These two questions are answered in the
  requirements process
• The requirements process consists of two
  activities
• Requirements Elicitation
• 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)

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Products of Requirements Process
(Activity Diagram)
Problem Statement
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System Specification vs Analysis Model

• Both models focus on the requirements from the
  users 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

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Requirements Analysis Document

• Introduction
• Current System
• Proposed System
• Functional requirements
• Nonfunctional requirements
• System Models
• Scenarios
• Use case model
• Object model
• Dynamic model
• User interface
• Glossary

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Requirements Elicitation

• Overview and Challenges
• Problem Statement
• Functional and Nonfunctional Requirements
• Requirements Validation Criteria

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Requirements Elicitation

• Very challenging activity
• Users dont know what they need the system to do.
  They could not articulate their needs.
• Users dont 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.

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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)
• 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
• Starts with Problem Statement

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Problem Statement

• 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
• A good problem statement describes
• 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

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Ingredients of a Problem Statement

• Current situation The Problem to be solved
• Description of one or more scenarios
• Requirements
• Functional and Nonfunctional requirements
• Constraints (pseudo requirements)
• Project Schedule
• Major milestones that involve interaction with
  the client including deadline for delivery of the
  system
• Target environment
• The environment in which the delivered system has
  to perform a specified set of system tests
• Client Acceptance Criteria
• Criteria for the system tests

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Categories of Projects

• 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
• 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
• Interface Engineering
• 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

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Types of Requirements

• Functional requirements
• Describe the interactions between the system and
  its environment independent from implementation
• Examples
• 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
• 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
• The implementation language must be Java

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Requirements Validation

• 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).

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Requirements Validation Criteria

• Completeness
• All possible scenarios through the system are
  described, including exceptions
• Consistency
• There are no contradicting requirements
• Clarity/Unambiguity
• The specification can only be interpreted one way
• Correctness
• Requirements represent accurately the system the
  client needs
• Realism
• The system can be implemented within constraints
• Verifiability
• Tests can be designed to demonstrate the system
  fulfills its requirements
• 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.

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Requirements Elicitation Activities

• Identifying Actors
• Identifying Scenarios
• Identifying Use Cases
• Refining Use Cases
• Identifying Relationships between Actors and Use
  Cases
• Identifying Initial Analysis Objects
• Identifying Nonfunctional Requirements

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Identifying Actors

• 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 systems 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

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Identifying Scenarios

• 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

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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?
• However, dont 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

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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.
• 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.

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Observations about Warehouse on Fire Scenario

• Concrete scenario
• Describes a single instance of reporting a fire
  incident.
• Does not describe all possible situations in
  which a fire can be reported.
• Participating actors
• Bob, Alice and John

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Another Example

• 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

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Observations about Web Server Failover Scenario

• Concrete scenario
• Describes a single instance of failover incident.
• Does not describe all possible situations in
  which failover can occur (e.g., server crashed,
  denial of service, etc).
• Participating actors
• Network Administrator, DNS

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Identifying Use Cases

• Use Case
• Specifies all possible scenarios for a given
  functionality
• Initiated by an actor
• 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
• Use Case Descriptions
• Entry and exit conditions
• Flow of events
• Quality requirements

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Heuristics How do I find use cases?

• Select a narrow vertical slice of the system
  (i.e. one scenario)
• Discuss it in detail with the user to understand
  the users preferred style of interaction
• Select a horizontal slice (i.e. many scenarios)
  to define the scope of the system.
• Discuss the scope with the user
• Use illustrative prototypes (mock-ups) as visual
  support
• Find out what the user does
• Task observation (Good)
• Questionnaires (Bad)

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Order of steps when formulating use cases

• 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
• 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

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Use Case Example ReportEmergency

• 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.
• Flow of Events on next slide.
• Special Requirements
• The FieldOfficers report is acknowledged within
  30 seconds. The selected response arrives no
  later than 30 seconds after it is sent by the
  Dispatcher.

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Use Case Example ReportEmergencyFlow of Events

• 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.

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Identifying Use Cases

• Writing Guide
• Choose proper name use verb phrases indicate
  users objective
• Name actors with noun phrases
• Clearly distinguish actors actions from systems
  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 ltltincludegtgt and ltltextendsgtgt relationships

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Refining Use Cases

• 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
• Refinements
• Details of objects in the system
• Low-level interactions between actors and system
• Access rights
• Missing exceptions
• Common functionality among use cases

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Refining Use Cases

• Heuristics
• Use scenarios to communicate with users and
  validate functionality
• Refine a single scenario to understand users
  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

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Relationships Between Actors and Use Cases

• Relationships between actors and use cases
• ltltinitiategtgt
• ltltparticipategtgt
• Determines access rights
• 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
• ltltincludegtgt
• For factoring out common functionality
• Explicitly invoked from the including use case
• ltltextendgtgt
• 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)

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ltltIncludegtgt Functional Decomposition

• Problem
• A function in the original problem statement is
  too complex to be solvable immediately
• Solution
• Describe the function as the aggregation of a
  set of simpler functions. The associated use case
  is decomposed into smaller use cases

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ltltIncludegtgt Reuse of Existing Functionality

• Problem
• There are already existing functions. How can we
  reuse them?
• 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)
• Example
• The use case ViewMap describes behavior that
  can be used by the use case OpenIncident
  (ViewMap is factored out)

Base Use Case
Supplier Use Case
Note The base case cannot exist alone. It is
always called with the supplier use case
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ltExtendgtgt Association for Use Cases

• Problem
• The functionality in the original problem
  statement needs to be extended.
• 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

Note The base use case can be executed without
the use case extension in extend associations.
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Generalization association in use cases

• Problem
• You have common behavior among use cases and want
  to factor this out.
• Solution
• The generalization association among use cases
  factors out common behavior. The child use cases
  inherit the behavior and meaning of the parent
  use case and add or override some behavior.
• Example
• Consider the use case ValidateUser, responsible
  for verifying the identity of the user. The
  customer might require two realizations
  CheckPassword and CheckFingerprint

Parent Case
Child Use Case
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Identifying Initial Analysis Objects

Le
v
el 1
Top Level Use Case
A and B are called Participating Objects
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Use Cases can be used by more than one object

Le
v
el 1
Top Level Use Case
Level 2 Use Cases
Le
v
el 2
Le
v
el 2
Level 3 Use Cases
Le
v
el 3
Le
v
el 3
Le
v
el 3
Operations
Le
v
el 4
Le
v
el 4
A
B
Participating Objects
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Identifying Initial Analysis Objects

• 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
• 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

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Identifying Nonfunctional Requirements(FURPS
Classification Scheme)

• Quality Requirements
• Usability
• Reliability/Dependability
• Safety
• Security
• Survivability
• Performance
• Response Time
• Throughput
• Availability
• Accuracy
• Supportability
• Adaptability
• Maintainability
• Portability

• Pseudo Requirements
• Implementation
• Interface
• Operations
• Packaging
• Legal

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Identifying Nonfunctional Requirements

• Heuristics
• Use a taxonomy (e.g., FURPS) to generate
  checklists
• Give different checklists to users in appropriate
  roles
• Checklists vary depending on application domain

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How to Specify a Use Case (Summary)

• Name of Use Case
• Actors
• Description of Actors involved in use case)
• Entry condition
• This use case starts when
• Flow of Events
• Free form, informal natural language
• Exit condition
• This use cases terminates when
• Exceptions
• Describe what happens if things go wrong
• Special Requirements
• Nonfunctional Requirements, Constraints)

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Managing Requirements Elicitation

• Negotiating specifications
• Maintaining traceability
• Tool support

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Negotiating Specifications (JAD)

• 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
• Leverages group dynamics of face-to-face meetings
• Developers get to understand application domain
• Users get to understand potential solution domain
  tradeoffs

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JAD Activities

• Project definition
• Facilitator determines objectives and scope of
  project through interviews with project manager
  and client
• Research
• 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

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JAD Activities

• Session
• Facilitator guides team in creating the
  requirements specification
• 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

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JAD Facilitator

• 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

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Maintaining Traceability

• 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

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Tool Support

• 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

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Summary

• The requirements process consists of requirements
  elicitation and analysis.
• The requirements elicitation activity is
  different for
• Greenfield Engineering, Reengineering, Interface
  Engineering
• Scenarios
• Great way to establish communication with client
• Different types of scenarios As-Is, visionary,
  evaluation and training
• Use cases Abstraction of scenarios
• Pure functional decomposition is bad
• Leads to unmaintainable code
• Pure object identification is bad
• May lead to wrong objects, wrong attributes,
  wrong methods
• 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?
• Use case modeling is a part of the requirements
  elicitation process, not the entire process
  itself.