An IDoc is a hierarchical structure that contains segments. Each IDoc segment has a header and data records. The header contains control information such as creation date and status. The control information is in an SAP structure called EDIDC.
When you add an IDoc source definition to a mapping, connect the IDoc source definition to an Application Source Qualifier. You can connect one IDoc source definition and other SAP tables to an Application Source Qualifier. You cannot connect more than one IDoc source definition to an Application Source Qualifier.