@startuml
skinparam monochrome true
skinparam packageStyle rectangle
skinparam shadowing true

title System Sequence Diagram US24 (SSD)

autonumber

actor "GSM" as GSM
participant ":System" as System

activate GSM

    GSM -> System : requests to Postpone an entry in the Agenda\n to a specific future date
    activate System

    System --> GSM : requests future date
    deactivate System

    GSM -> System : enters future date
    activate System

    System --> GSM : updated entry
    deactivate System

@enduml