I. Use Case Model: Drawing System Sequence Diagrams (Larman Ch. 9)
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 SYSTEM SEQUENCE DIAGRAMS (SSDs) (CH. 9)

Goal:
  - identify system events
  - frame system as a "black box"
  - understand system behavior better

Do these for:
  - main success scenario
  - frequent or complex alternatives

Example:
  O 
 \|/                           |---------|
 / \   Process Sale Scenario   | :System |
:Cashier                       |---------|

  |       makeNewSale()            |
  |------------------------------->|
  |                                |
  |  enterItem(itemID, quantity)   |
  |------------------------------->|
  |                                |
  |     description, total         |
  |<-------------------------------|
  |        *[more items]           |
  |                                |
  |         endSale()              |
  |------------------------------->|
  |                                |
  |       totalWithTaxes           |
  |<-------------------------------|
  |                                |
  |       makePayment(amount)      |
  |------------------------------->|
  |                                |
  |     changeDue, receipt         |
  |<-------------------------------|
  
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 A. System boundary (9.6)
        Where's the system boundary here?
 B. Naming system events and operations (9.7)
   Which is better as a system event name: "enterItem" or "scan"?
 C. practice
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       FOR YOU TO DO (IN TEAMS)

Create one or two SSDs for
your main use cases
(ones you'll use in the first iteration).
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 D. Showing use case text (9.8)
 E. Questions
   Is a necessary to create SSDs for all scenarios of all use
   cases?
   how long should you spend creating SSDs?