ALE provides a complete programming model for implementing BAPIs. ALE supports these method calls:

• Synchronous method calls

Synchronous method calls can also be used in ALE distribution scenarios. These method calls are either BAPIs or Dialog Methods [Seite 191].In ALE Customizing you can assign the RFC destinations to be used for a synchronous method call.

• Asynchronous method calls

If BAPIs are called asynchronously, ALE error handling and ALE audit can be used.If an asynchronous BAPI call is to be used for the distribution, the BAPI-ALE interface required for inbound and outbound processing can be automatically generated. Developing an ALE business process in ABAP is restricted to the programming of the BAPI.

An object-oriented approach has the following advantages:
- The application only has to maintain one interface
- The automatic generation of the BAPI-ALE interface avoids programming errors.

Process Flow

If you are not enhancing an SAP BAPI and you are not creating your own BAPI when you are implementing an ALE business process, you can simply follow the steps below:
• Filtering Data
• Determining the BAPI Receivers

If, on the other hand, you want to enhance a BAPI or create your own, you have to follow these steps:

• Implementing Your Own BAPIs
• Maintaining the BAPI-ALE Interface
• Determining the BAPI Receivers Application programs must call a function module for the receiver determination and a generated application function module in the BAPI-ALE interface.You can verify the quality of the ALE layer and ALE business processes using Automatic Tests.

BAPIs can be called by applications synchronously or asynchronously. ALE functions such as BAPI maintenance in the distribution model and receiver determination can be used for both types of call.Note that synchronously-called BAPIs are only used for reading external data to avoid database inconsistencies arising from communication errors.

The application synchronously calls a BAPI in the external system to create an FI document. The document is correctly created but the network crashes whilst the BAPI is being executed. An error message is returned to the application and the FI document is created again.The document has been duplicated in the system called.An application program can implement a two-phase commit by thoroughly checking the data in the external system.An easier solution is to call the BAPI asynchronously, as Error Handling assures that the data remains consistent.
A BAPI should be implemented as an asynchronous interface, if one of the criteria below applies:

• Consistent database changes in both systems

Data must be updated in the local system as well as on a remote system
• Loose coupling

An asynchronous interface would represent too narrow a coupling between the client and the server systems. If the connection fails the client system can no longer function correctly.

• Performance load

The interface is used often or it handles large volumes of data. A synchronous interface cannot be used in this situation because performance would be too low.If you want to implement a BAPI as an asynchronous interface, you have to generate a BAPI-ALE interface for an existing BAPI.



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