Requirements Analysis

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Requirements Analysis
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Requirements Reflect Users View

• Requirements are defined in terms of
• Actors the different types of users
• Use Cases the tasks users perform with the
  system
• Scenarios possible outcomes from the use cases

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The Process of Use case Analysis

• Define the user roles in the system
• Define the use cases of each user role
• Define the scenarios for each use case

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Identify the Roles Users Play

• Actors represent the roles a user can play
• Actors model anything that communicates with the
  system
• An actor can be another computer system
• Actors represent what is outside the system.

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ATM system

• Identifying actors
• Human users what roles do users paly in the
  system?
• What use cases do the users perform?
• Do other systems interact with this system?

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Actors in the ATM System

• Customer
• Repair Engineer
• Bank System

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Actors Initiate Use Cases

• A use case is a piece of functionality offered by
  the system
• It describes a complete course of events or
  athread of control through the system
• Use cases are defined from the perspective of the
  user
• The complete set of use cases defines the system
  functionality.

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Identifying use cases

• By detrmining the tasks of each actor.
• Interviewing end users and domain experts
• Example
• Actor Customer
• Withdraw money
• Deposit money
• check balanc

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• Actor repair Engineer
• Fix Printer
• Fix Display
• Actor Bank System
• Notify Bamk system that system will be
  unavailable

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Detailing Use Cases

• Define the basic case of the use case
• The basic case represents the most usual
  execution of the use case
• Answer the following questions
• Does the actor input data to the system?
• Does the actor need responses from the system?
• Does the system need to request information from
  the actor during the execution of the use case?

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ATM Withdraw

• Customers inserts card. The system retrieves the
  customer information from the card.
• The system requests PIN number and validates the
  PIN number.
• Customer selects withdraw
• The system requests the account to withdraw from
  and amount.

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.

• The system sends debit request to the bank
  system. The bank system validates the request The
  system counts the money and prints the receipt.

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Scenarios

• Represent an instance of the use case.
• Act as test cases for the use cases.
• Example Possible scenarios for withdraw are
• User inserts invaid card
• User enters wrong PIN
• User Does not have adequate funds
• User cancels transaction

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User enters wrong PIN

• Notify user that wrong PIN has been entered
• Allow the user three attempts
• After the third attempt return card to the user.