Two types of communication, often used terms in interfacing country. What are they ? What's the difference ?
EDI - Electronic Data Interchange application documents (e.g. the Purchase Order) are transformed (copied) into an electronic state (an Idoc) and handed over to the gates of the system as a file. The file is then transferred somewhere to be interpreted again. Hence EDI for R/3 is based on Idoc and Idoc processing
ALE - Application Link Enabling .. where EDI left of, only a bit more advanced. The concept of electronic data interchange is taken further to actual "Application document in the sending system" to "Application document in the receiving system" before the ALE link completes. With ALE, an Idoc is created and passed to an RFC port rather than a File port. So instead of creating a file, a direct link is made to the receiving system implicating that the receiving system receives at the same time the sending sysyem sends. Typically SAP to SAP communication, however some other tools (MQSI) can receive an Idoc via RFC as well.