Maintaining the Distribution Model
The distribution model describes the ALE message flow between logical systems - that is, it determines which messages are distributed to which logical systems. This BAPI-based distribution of data to recipients can be restricted according to your specific requirements.
For example, you can make distribution dependent on conditions that you define as filters in the ALE distribution model (through the Implementation Guide:
Basis 
Application Link Enabling (ALE) Model and Implement Business Processes Maintain Distribution Model 
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The prerequisite for this is that a filter object type has been assigned to the corresponding BAPI in the SAP application. For some BAPIs, SAP has already defined and assigned filter object types. You can also define your own filter object types and assign them to a BAPI. For more information on defining filter objects, refer to the document "ALE Introduction and Administration" under Modeling Distribution .
We differentiate between different types of filtering for BAPIs:
Receiver Filtering
Before the BAPI or generated BAPI-ALE interface can be called, the receiver must be determined. To link the receiver determination with conditions, the business object methods are assigned to filter object types during receiver filtering. The values of these objects are used to determine the permitted receivers. The valid filter object values must be defined in the distribution model.
In the ALE distribution model the following dependencies can be mapped:
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Between a BAPI and a message type
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Between BAPIs
If such a dependency is defined as a condition in the ALE distribution model, the receiver of the referenced BAPI or message type is determined.
For more information on receiver filtering when using BAPIs, refer to the ALE Programming Guide under Determining Receivers for a BAPI .
Data Filtering
Two data filtering services are provided for asynchronous BAPI calls via the BAPI-ALE interface:
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Interface reduction
The BAPI reduction does not have any conditions - it is a projection of the BAPI interface.
The BAPI reduction dodes not have any conditions - it is a projection of the BAPI interface. The developer of the BAPI whose interface is to be reduced must create the BAPI as a reducible using appropriate parameter types.
If you reduce the BAPI interface, you do not have to define any filter object types.
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Parameter filtering
The BAPI parameter filtering is linked to conditions and is therefore content-dependent: The lines in table parameters of asynchronous BAPIs are determined depending on the values in the lines (or dependent lines) for the receiver. The table dataset of a BAPI is determined for parameter filtering. Hierarchical relationships can also be defined between table parameters of the BAPI. To implement parameter filtering, business object methods are assigned to the business object method of filter object types. The valid filter object values must be defined in the distribution model.
For more information on data filtering and BAPIs, see the ALE Programmer Guide under Data Filtering .
BAPI filtering is the term used for the shared use of both the filter services of the BAPI interface. BAPI filtering is implemented as a service in ALE outbound processing.