Use Case Path Interaction Requirements

Definition

A use case path interaction requirement is a functional requirement that specifies a single required interaction between the blackbox business enterprise, application, and component and an external during the execution of a use case path.

Objectives

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

• Ensure that the enterprise, application, or component interacts successfully with the external.
• Enable use case models to be used for the analysis and specification of functional requirements.

Examples

The following are typical examples of use case path interaction requirements:

• Automatic Teller Machine:
  • Actor: Account Holder.
  • Use Case: Withdraw Funds.
  • Normal Use Case Path: Successful Withdrawal.
  • Interactions (whereby interactions 2, 4, 6, 7, and 8 specify path requirements):
    1. “The authenticated account holder requests the withdrawal of funds from the ATM.”
    2. “The ATM shall respond by requesting the following information from the account holder:
       • The account from which to withdraw the funds.
       • The withdrawal amount.”
    3. “The account holder responds by entering the following information:
       • The account from which to withdraw the funds.
       • The withdrawal amount.”
    4. “The ATM shall respond by sending a withdrawal request containing the following information to the bank computer:
       • The account from which to withdraw the funds.
       • The withdrawal amount.
       • The transaction number.
       • The ATM identifier.”
    5. “The bank computer responds by sending a withdrawal approval message containing the following information to the ATM:
       • The account from which the funds were withdrawn.
       • The initial account balance.
       • The withdrawal amount.
       • The new account balance.
       • The transaction number.
       • The ATM identifier.”
    6. “The ATM shall respond by dispensing the withdrawal amount to the account holder.
    7. “The ATM shall respond by dispensing a transaction receipt containing the following information to the account holder:
       • The ATM location.
       • The date and time.
       • The account from which the funds were withdrawn.
       • The initial account balance.
       • The withdrawal amount.
       • The new account balance.
       • The transaction number.”
    8. “The ATM shall respond by requesting if the account holder requests any additional transactions.
• Digital Thermostat Example:
  • Actor: User.
  • Use Case: Set Desired Temperature.
  • Normal Use Case Path: Increase Desired Temperature.
  • Interactions (whereby interaction 2 specifies a path requirement):
    1. “The user notifies the digital thermostat of a new increased desired room temperature.”
    2. “The digital thermostat shall respond by displaying the new desired room temperature to the user.”
• Global Personal Marketplace (GPM), an Online Auction Example:
  • Actor: Buyer.
  • Use Case: Buyer Places Bid.
  • Normal Use Case Path: Single Bid Placed.
  • Interactions (whereby interactions 2 and 4 specify path requirements):
    1. “The buyer notifies the GPM that he/she wants to place a bid.”
    2. “The GPM shall respond by requesting the following information from the buyer:
       • The type of bid (single bid).
       • The bid amount.
       • The desired quantity.”
    3. “The buyer sends a submit bid request with the following information to the GPM:
       • The type of bid (single bid).
       • The bid amount.
       • The desired quantity.”
    4. “The GPM shall respond by sending a notification containing the following information to the buyer:
       • The ‘Single Bid Placed’ message.
       • The bid amount.
       • The desired quantity.”
    5. “The buyer sends a notification acknowledgement to the GPM.”

Guidelines

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

• Note that only those interactions initiated by the business, application, or component specify path interaction requirements. Requirements cannot specify requirements on externals, but only on how the business, application, or component must interact with these externals. Thus, external-initiated interactions set up local preconditions for path interaction requirements.
• See additional use case path guidelines.