The data content of a business object describes the information that can be created, updated, deleted, and asked for by the business object. The description is made using a reference to the data model (table objects, relationships etc.) to be made or already made.
Data elements can be owned or shared by business objects. A data element can only be owned by ONE business object.
An example of the data contents of a business object order is the table object order plus the table object order line. The business object should also own or share the domains of these two table objects and will typically own the relationship between order and order line. The relation between order and customer will be owned by the business object customer.
Before you can define the data contents of a business object you have to understand the principles of making a relational or object oriented data model.