Want to Learn Siebel EAI ??? Part1

I have seen many of my friends who want to learn Siebel EAI but not sure of where to begin with??
Lets start with few simple Qs,
           -What is EAI-Enterprse Application Integration ?
           -Why EAI ?                                                                                      
           -What are the benefits/Advantages of EAI ?

EAI is essential to Share the Data between 2 or more Applications. Data may be centralized or may have spread across various Applications but data sharing is essential in achieving efficienct,Cost Effective implemenation .The data share may happen in various ways either Synchronous(Online) or Asynchronous(Offline) or batch load.
Any EAI Implementaion basically concentrates on...
1.What kind of Integration Architecure ?
2.What kind of Data Shared?
3.Which Type of Target Application- Portal/Java/Mainframe??
4.Data Flow Across Applications
5.Primary Data Source.
6.Available Integration Techniques
Continued.....