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Since it requires very tight coupling with EIS A, EAI application 1 bypasses

the J2EE application server but reuses the connector layer. Application 2 needs to

use some business logic present in the application server. As a result, it does not

want to access the EIS directly. Application 2 instead uses a combination of syn 

chronous and asynchronous calls to the EJB tier. These calls (to enterprise beans

and message driven beans) access EIS A and the relational database through

JDBC, EJB container managed persistence, or connectors. EIS B also generates

asynchronous messages for implementing the business logic, and these messages

must be delivered to a message driven bean. Application 3 uses the least tightly

coupled interface, Web services, and it accesses available functionality through a

Web service interface. The Web service internally uses the business logic stored in

the J2EE application server. (In the next sections we take a closer look at these

different EAI design approaches and then provide some guidelines for implement 

ing these approaches.)

Let's see how you might apply this strategy to the adventure builder enter 

prise. The adventure builder enterprise decides to use several layers for

integration:

1. Web services as an integration layer for its supply chain. 

2. Web services as an integration layer for communicating among different de 

partments. For example, the adventure builder Web site uses a Web service to

send an order to the order processing center. 

3. EJB/JMS components as the integration layer with EISs. The order processing 

center integrates EISs within its department using JMS. Hence, the order pro 

cessing center fulfills an order using JMS and EJB technologies for integrating 

its various EIS systems, customer relations management, billing systems, and 

so forth. 

6.3.1 Web Services Approach

One approach for EAI is to use a Web service as the integration layer. With this

approach, an enterprise's EIS systems expose their functionality by implementing

Web services. They make their Web service interfaces available to other applica 

tions by providing WSDL descriptions of them. In addition, the integration layer

may also include XML schemas for the documents used as parameters and return

values. Essentially, the WSDL description of the service interface and document

schemas becomes the integration layer, or the point of stability.