ALE: is nothing but application link enabling is used to
connect with the non sap systems to the sap systems. and
also the used to connect with the legacy systems with the
sap systems. just its a link between the two process.

IDOC; is nothing but intermediate document. IT is the
container of the message. idoc can be transferred between
the two process to send the data or container of the
message. Every idoc have three types of records.
these three types are records are given below.

----> data record
----> control record
----> status record
data record: is contains administration data header data 
and item data.

control record: is contains of sender information reciever
information , message type, idoc type , idoc number.

status record: is contains of all the status of idocs. 

process steps:

-->define the logical systems                           
-->assign the logical systems to the respective clients
-->define the RFC destination
-->create the customer distribution model
-->create the patner profile
-->creat the port
-->create the message type
-->assign the message type into the idoc type
--> to check the status of idocs.