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What do you mean by use or access , Start process starts child process asynchronously , you can initially pass data . But you can't maintain the relationship. Can you tell more about What you want to know. In Child process you are not getting data??
https://docs.appian.com/suite/help/24.1/Ways_to_Start_a_Process_From_a_Process.html#comparing-ways-to-start-a-process-from-a-process