This is a very useful material from a consulting firm

Contents: 

Chapter 1 – ALE Overview 
Chapter 2 – Introduction to IDocs 
Chapter 3 – Modeling ALE Distribution 
Chapter 4 – Communication Parameters
Chapter 5 – ALE Architecture
Chapter 6 – Data Distribution Methods
Chapter 7 – ALE Monitoring
Chapter 8 – Error Handling
Chapter 9 – Using ALE for Interfaces
Chapter 10 – IDoc Processing Features
Chapter 11 – ALE Performance
Chapter 12 – IDoc Reduction
Chapter 13 – IDoc Extension
Chapter 14 – IDoc Creation
Chapter 15 – IDoc Processing

Download SAP ALE Training Program