Application Link Enabling (ALE) allows business data (and thus costing data) to be distributed between multiple, loosely-linked R/3 systems. It also connects R/2 systems to external systems, and distributes data between different Releases.

ALE aims to decentralize business applications while maintaining data consistency. The reasons for this decentralization can include the following:

• The globalization of markets, and the separation of organizational units
• Increase in the performance capacity of an R/3 system
• Business processes that are not restricted to a single company and which include customers and vendors

ALE consists of a controlled exchange of messages between distributed applications. To set up a distribution of business processes and functions with ALE, you must create a logical distribution model for the entire system. The distribution model describes the ALE message flow between logical systems. It contains the relationships between logical systems, message types, BAPIs, and filters. In the model, you determine which applications run on which systems, and which messages exchange applications with each other. You specify the following:

• Which applications run on which systems
• Which master data and transaction data should be exchanged
• Which control data should be made known to the distributed systems

In the distribution model, you specify which messages should be sent to which logical system. In addition, filters enable you to define conditions for the content and sending of messages.

The Idoc (intermediate document) is the basis for the exchange of data. An Idoc is a container for the exchange of data between R/3, R/2 and/or external systems. Whereas ALE uses Idocs to communicate data between logical systems, external systems can use them as standard interfaces for data transfer.

Business data, functions and processes can be distributed in two different ways, depending on the type of message sent:

• Distribution by message type
• Distribution via BAPIs

There are also tools available in ALE for the monitoring and setting of ALE functions.

• The ALE audit enables the sending R/3 system to monitor the processing status of the Idoc sent to the receiving system. The receiving system sends completion confirmations to the sending system.
• You can optimize the system performance of ALE processing by controlling the periodic flow, processing Idocs in parallel, and by package processing.
• ALE serialization functions control the sequence of processing the IDocs.