the basic difference between ALE and EDI is as follows
Application Link Enabling (ALE)
You distribute data using ALE if you want to communicate from one system to one or more other (mostly internal) systems. ALE transfers data in IDoc format and uses the methods of tRFC for data transfer.
ALE enables the integration of business processes across several SAP or non-SAP systems
Electronic Data Interchange (EDI)
You use EDI if you want to exchange business application documents with an (external) partner system (for example, a customer or vendor). The SAP system sends EDI messages in IDoc format to an EDI subsystem, where they are converted to a universal EDI standard (UN/EDIFACT or ANSI/X12). This enables communication with non-SAP systems.
By definition, two partners are involved in the process in an EDI application scenario: The sender and the recipient of an EDI message
