Introduction – ALE – Application Link Enabling
ALE can be used to integrate business processes and data between SAP systems or SAP and non SAP systems.
Data is exchanged asynchronously, whereby the data arrives in the receiver system, even if the receiver system cannot be connected to at the time the data is sent.
Communication occurs with BAPI’s (Business Application Programming Interfaces) or IDocs (Information Documents)
Synchronous connections are only used by ALE to read data.
The SAP online help for ALE is here
You can access ALE settings through: SAP menu–>Tools–>ALE
As well as the Transaction SALE.