Download a nice presentaion from this link given below.
http://www.slideshare.net/shesagiri/ale-idoc-edi/
This is a very nice presentation available on net.
Other Useful Link :
Useful Guide to ALE, IDOCs
IDoc Interface: EDI
IDoc Connector for XML Component (BC-FES-AIT)
IDoc Class Library (BC-FES-AIT)
Other Useful Link :