What is EAI , purpose of EAI and EAI Patterns?

Enterprise Application Integration (EAI) is defined as the use of software and computer systems architectural principles to integrate a set of enterprise computer applications.

Purposes of EAI:
EAI can be used for different purposes:
* Data (information) Integration: Ensuring that information in multiple systems is kept consistent. This is also known as EII (Enterprise Information Integration).
* Vendor independence: Extracting business policies or rules from applications and implementing them in the EAI system, so that even if one of the business applications is replaced with a different vendor's application, the business rules do not have to be re-implemented.
* Common Facade: An EAI system could front-end a cluster of applications, providing a single consistent access interface to these applications and shielding users from having to learn to interact with different software packages.

Integration patterns

There are two patterns that EAI systems implement:

Mediation:

Here, the EAI system acts as the go-between or broker between (interface or communicating) multiple applications. Whenever an interesting event occurs in an application (e. g., new information created, new transaction completed, etc.) an integration module in the EAI system is notified. The module then propagates the changes to other relevant applications.

Federation:

In this case, the EAI system acts as the overarching facade across multiple applications. All from the 'outside world' to any of the applications are front-ended by the EAI system. The EAI system is configured to expose only the relevant information and interfaces of the underlying applications to the outside world, and performs all interactions with the underlying applications on behalf of the requester.

Both patterns are often used concurrently. The same EAI system could be keeping multiple applications in sync (mediation), while servicing requests from external users against these applications (federation).

Access patterns

EAI supports both asynchronous and synchronous accesss patterns, the former being typical in the mediation case and the latter in the federation case.

Lifetime patterns

An integration operation could be short-lived (e. g., keeping data in sync across two applications could be completed within a second) or long-lived (e. g., one of the steps could involve the EAI system interacting with a human work flow application for approval of a loan that takes hours or days to complete).