A message is a data structure that a flow uses to store data into and recover data from while the flow is being performed (see Working with messages).
An element of a message (or the equivalent term message element ) is a component of a message:
A complex data type can contain include fields belonging to simple data types and structures belonging to complex data types.
Note also that:
A literal value can serve as the source element of a mapping (see One-sided mapping).
In the mapping editor, a target element can serve as the source element of a mapping. However, the target element of such a mapping must also (as always) be a target element.
For example, suppose that v_CatalogRequest and o_CatalogRequest are target messages (they are located on the right side of the mapping routine area) and each contains fields named intRequestID and intOrderID. Then a mapping from v_CatalogRequest.intRequestID to v_CatalogRequest.intOrderID, or any similar mapping, is valid.