5.3 系統順序圖


系統順序圖 System Sequence Diagram

   把待建系統看成一個黑盒子,研究參與者與系統邊界的交互
   SSD

     System Sequence Diagram

   What is SSD

     A SSD is a picture that shows, for one particular scenario of a use case, the events that external actors generate, inter-system events , and their order

     All systems are treated as a black box

     the emphasis of the diagram is events that cross the system boundary from actors to systems

   System Event

     external input events

       actor generates events to a system

   system operation

     to handle the system event , for example

       when a cashier enters an item's ID, the cashier is requesting the POS system to record that item's sale (the enterItem event). That event initiates an operation upon the system


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