The purpose of the ProcessChartOfAccounts is to enable an application to request specific ChartOfAccounts information from another business application module.  The response to the ProcessChartOfAccounts is the ShowChartOfAccounts.
DataArea [1..1] Is where the information that the BOD message carries is provided, in this case ProcessChartOfAccounts. The information consists of a Verb and one or more Nouns. The verb (Process) indicates the action to be performed on the Noun (ChartOfAccounts).