系统顺序图的组成 system as black box the name could be"NextGenPOS" but"System"keeps it the",and underline imply an instance, and are explained in a later chapter on sequence diagram notation in the UML external actor to Process sale scenario o Cashier System make Sale UML loop interaction Item(temID, quantity) frame. with a boolean guard expression description total endsale parameters associated with the total with taxes it is an abstraction system event of an abstraction that entering the ignores presentation makePayment(amount and medium payment data by some mechanism the return line is change due, recei optional if nothing is returned系统顺序图的组成 enterItem(itemID, quantity) : Cashier :System endSale makePayment(amount) a UML loop interaction frame, with a boolean guard expression external actor to system Process Sale Scenario system as black box the name could be "NextGenPOS" but "System" keeps it simple the ":" and underline imply an instance, and are explained in a later chapter on sequence diagram notation in the UML a message with parameters it is an abstraction representing the system event of entering the payment data by some mechanism description, total return value(s) associated with the previous message an abstraction that ignores presentation and medium the return line is optional if nothing is returned total with taxes change due, receipt makeNewSale loop [ more items ]