Use Case Path Requirements

Definition

A use case path requirement is a functional requirement that specifies a single path thorugh a use case that shall be implemented by a single:

• Business Enterprise.
• Application.
• Component.

Objectives

The typical objectives of a use case path requirement are to:

• Ensure that the application or component successfully provides the required use case path functionality to a specific external (e.g., human actor, external application).
• Enable use case models to be used for the analysis and specification of functional requirements.

Examples

The following are typical examples of use case requirements:

• Automatic Teller Machine:
  • Normal Path: Successful Withdrawal.
    “The ATM shall enable an account holder to withdraw an account-holder specified amount of funds from an associated account if:
    • The withdrawal amount is the some of one or more $20 bills.
    • The withdrawal will not make the account overdrawn.
    • The withdrawal when added with previous withdrawals for the day will not exceed the maximum daily account withdrawal limit.
    • There is no hold on the account.”
  • Normal Path: Successful Fash-Cash Withdrawal.
    “The ATM shall enable an account holder to withdraw a specified amount of funds from an associated account if:
    • The withdrawal amount is one of the system specified amounts of $20, $40, $100, or $200.
    • The withdrawal will not make the account overdrawn.
    • The withdrawal when added with previous withdrawals for the day will not exceed the maximum daily account withdrawal limit.
    • There is no hold on the account.”
  • Exceptional Path: Account Overdrawn.
    “The ATM shall not enable an account holder to withdraw any amount of funds from an associated account if the account is currently overdrawn.”
  • Exceptional Path: Account Becomes Overdrawn.
    “The ATM shall not enable an account holder to withdraw any amount of funds from an associated account if the withdrawal amount will make the account overdrawn.”
• Digital Thermostat Example:
  • Normal Path: Increase Desired Temperature.
    “When turned on, the digital thermostat shall enable the user to increase the current desired temperature of the room by an increment of integral degrees to a temperature of up to and including the maximum allowed temperature for the current temperature scale.”
  • Normal Path: Decrease Desired Temperature.
    “When turned on, the digital thermostat shall enable the user to decrease the current desired temperature of the room by an decrement of integral degrees to a temperature of down to and including the minimum allowed temperature for the current temperature scale.”
  • Exceptional Path: Digital Thermostat Turned Off.
    “When turned off, the digital thermostat shall not enable the user to change the current desired temperature of the room”
  • Normal Path: Decrease Desired Temperature.
    “When turned on, the digital thermostat shall enable the user to decrease the current desired temperature of the room by an decrement of integral degrees to a temperature of down to and including the minimum allowed temperature for the current temperature scale.”
  • Normal Path: Maintain Desired Temperature.
    “The digital thermostat shall control the air conditioner and furnace to maintain the actual temperature of the room within engineering tolerances of the desired temperature of the room.”
  • Normal Path: Air Conditioner Failed.
    “The digital thermostat shall notify the user if the air conditioner fails.”
• Global Personal Marketplace (GPM), an Online Auction Example:
  • Normal Path: Single Bid Placed.
    “The GPM shall enable a buyer to place a single new bid on an auction if:
    • The new bid is at or above the minimum bid amount.
    • The new bid increment is at or above the minimum bid increment amount.
    • The bid is not for more items than are currently available for auction.
    • The auction is open.”
  • Normal Path: Automatic Proxy Bid Placed.
    “The GPM shall enable a buyer to establish an automatic proxy bid if:
    • The initial proxy bid is at or above the minimum bid amount.
    • The new proxy bid increment is at or above the minimum bid increment amount.
    • The proxy bid is not for more items than are currently available for auction.
    • The auction is open.”
  • Normal Path: Instant Win Price Bid.
    “The GPM shall enable a buyer to place a single instant win bid if:
    • The bid is equal to the instant win bid amount.
    • The bid is not for more items than are currently available for auction.
    • The auction is open.”
  • Exceptional Path: Bid Below Minimum Bid.
    “The GPM shall not enable a buyer to place a bid of any kind if the bid is below the minimum bid amount.”
  • Exceptional Path: Bid Increment Below Minimum Bid Increment.
    “The GPM shall not enable a buyer to place a bid of any kind if the bid increment is below the minimum bid increment amount.”
  • Exceptional Path: Excessive Quantity Requested.
    “The GPM shall not enable a buyer to place a bid of any kind if the bid is for more items than are currently available for auction.”
  • Exceptional Path: Auction Closed.
    “The GPM shall not enable a buyer to place a bid of any kind on an auction if the auction is closed.”

Guidelines

The following guidelines have been found to be useful when producing use case requirements:

• Because use case paths involve multiple interactions and postconditions, individual use case path requirements are too general to be specifically testable without being further refined at the use case path level.
• Use case path requirements should always include:
  • The external that benefits from the proper execution of the use case.
  • The preconditions required to go down that path.
• See additional use case path guidelines.