Use the Column Mapping tab of the Logical Table Source dialog to map logical columns to physical columns.
The physical to logical mapping can also be used to specify transformations that occur between the Physical layer and the Business Model and Mapping layer. The transformations can be simple, such as changing an integer data type to a character, or more complex, such as applying a formula to find a percentage of sales per unit of population. Applying these transformations is typically referred to as creating calculated items.
The data type of a logical column is determined by its logical table source mappings. For example, if a logical column has one physical source with a data type of VARCHAR(50) not-nullable, and another physical source with a data type of VARCHAR(20), nullable, then the data type of the logical column is VARCHAR(50) nullable. This final type is called a promoted type. Because of the rules governing logical table source mappings, you cannot map physical sources with data types that cannot be promoted such as an INT with a VARCHAR.
You can edit the logical table sources from which the column derives its data, or unmap it from its sources.
In the Logical Column dialog, the Column Source tab contains information about the logical column.