@startuml rectangle “A Student” as S rectangle “Online Book Ordering System” as OBOS rectangle “Fulfillment Center” as FC rectangle “Books” as B rectangle “Book Order” as BO S -right->> OBOS: 1: login OBOS -down- B OBOS -down->> FC: 2: submit books\n3: calculate price FC -- B FC -down- BO: 4: get quantity B -right- BO @enduml