The business object relationships contain only table references that make up the object. Often parts of the object definition are linked through relationships to other data in other tables that expand on some of the information of the data elements of the table. This is very common, linking customer- id to expanded customer information, part-number to expanded product description, personnel-id to identify the actual person involved. The tables linked to are not part of the business object; they merely provide expanded information. These are referred to as reference tables.
There are two distinct cases for reference information. The first case is where the referenced information is not part of the application. The second case is where the application structure is divided into multiple streams to archive transactions earlier than master information would be archived. In this case some of the master information might be designated as a reference for a subordinate table.