To replicate a business object instance, for example, to transfer data between two distributed systems in the context of Application Link Enabling (ALE), you can implement specific standardized BAPIs.

The objective of replicating business object types is to make specific instances of an object type available on one or more additional systems. The replicated instances are usually created under the same object key.

The interface of these BAPIs depends on the characteristics and contents of the business object that is to be replicated. For this reason replicate BAPIs must be implemented for each business object.

Business objects instances can be replicated in two ways:

• Upon request ("Pull)
  System "A" requests replicates from system "B". Then system "B" replicates the requested business object instances on system "A".

• Via subscription list ("Push")
  In this approach system "B" maintains a list of systems requiring replicates. At regular intervals, system "B" replicates the business object instances to all the systems in the list.

Both of the above replication methods can be implemented with the BAPIs Replicate(), SaveReplica() and SaveReplicaMultiple(). These BAPIs are both class methods (instance-independent).

The BAPI Replicate() is called in the system which contains the originals of the business object instances to be replicated. The BAPI Replicate() is used for:

• Identifying the business object instances to be replicated and to organize the required data

• Calling the SaveReplica() methods in the receiving system

The BAPI Replicate() can only request the replication of instances of a business object. The actual replication is carried out when the server system calls one of the SaveReplica() BAPIs described below on the client system.

You must follow the steps below:

1. Select the data to be replicated.

2. Determine the receiver.

3. Loop via the receiver and call the relevant SaveReplica() BAPI.

4. Enter a value in the Return parameter and complete the Replicate() BAPI.

The interface of the Replicate() BAPI must contain the following parameters:

• Parameters which identify the business object instances to be replicated

• Parameter Recipients

• If customers are to be enabled to enhance the import parameters of the BAPI without modifications being necessary, you must create the parameter ExtensionIn.

The interface of the Replicate() BAPI can also contain the following parameters:

• Parameter RequestChanges

• ‘ ‘ (no value):
  No value is the standard setting and means that engineering change management will not be accessed.

• ‘X’:
  This value means that the modified data is replicated directly from engineering change management.

• Other BAPI-specific import parameters, for example, to specify the data range of the instances to be replicated (for example, material with or without plant data).

The BAPI Replicate() should contain the following export parameters:

• The Return parameter in which messages from the method call are returned to the calling program.

• A table containing information on the object instances to be replicated.

• If customers are to be allowed to extend the export parameters of the BAPI without modifications being necessary, you must create the parameter ExtensionOut.

The class method SaveReplica() and the method SaveReplicaMultiple() generate replicates of business object instances. They are used to replicate objects in different systems that are semantically identical. For technical reasons these objects may be created with different objects keys (object IDs).

The BAPI SaveReplica() is used by a system to replicate one business object instance on a target system or to modify one business object that has already been replicated. Whilst the SaveReplicaMultiple() BAPI can replicate several business object instances on the target system or modify several instances that have already been replicated.

For each business object type to be replicated you have to implement one or both of these methods, according to your requirements.

You should keep the following points in mind when defining the import parameters:

• For the SaveReplica() BAPI, all the data required for replicating an individual business object instance must be provided in the import parameters. For the SaveReplicaMultiple() BAPI, all the relevant data for replicating several instances must be provided in the import parameters. All business object information may be provided, it must, however, be able to be derived. Since these are class methods, none of the BOR key fields may be a parameter in the function module or of the BAPI.

• If only parts of objects are to be replicated rather than whole objects, you can use other optional import parameters.

• The BAPI must also have a TestRun parameter that enables it to execute test runs. If this parameter is filled with the value "X", the BAPI executes normally, but does not write the results to the update task. In this way, after the BAPI BapiService.TransactionCommit executes, all results, such as the application log, for example, can be evaluated, but the BAPI has not modified the database.

You should keep the following points in mind when defining the export parameters:

• If customers are to be allowed to extend the export parameters of the BAPI without modifications being necessary, you must create the parameter ExtensionOut.

• To report messages from the method call back to the calling program, you should create the parameter Return. To ensure the results of a SaveReplica() BAPI, called either synchronously or asynchronously, are monitored extensively, the following conventions for filling the Return parameter must be observed:

• If the SaveReplica() BAPI executes successfully, the following standardized T100 message must be passed in the Return parameter:

• The field MESSAGE_V1 contains the external name of the business object type, such as SalesOrder.

• The information identifying the replicated object is returned in MESSAGE_V2.

• If an error occurs during the execution of the SaveReplica() BAPI, in addition to the application-specific error messages the following standardized message must be passed in the Return parameter:

• In addition to the standardized message, further messages can be written in the Return parameter. It is of particular importance when errors occur that messages describing the errors in detail are returned. You should, therefore, use all of the fields of the structure BAPIRET2. You should, in particular, fill the fields Parameter, Row and Field.