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A J2EE application may be configured in a number of different ways to access an enterprise information system. The following sections illustrate a few typical enterprise information system integration scenarios.
The sample application illustrates an Internet E-Store application. Company A deploys the sample application to create an Internet E-Store. The application is composed of a set of enterprise beans, JSP pages, and servlets that collaborate to provide the overall functionality of the application. The database stores data related to product catalogs, shopping carts, customer registration and profiles, and order status.
The architecture of this application is illustrated in Figure 6.1.
A customer uses a Web browser to initiate an e-commerce transaction with the sample application. A customer
Company A stores all persistent information about customers and their transactions in an existing database that already contains product and inventory information.
Company B has developed and deployed an employee self-service application based on the J2EE platform. This application supports a Web interface to existing human resources applications supported by the enterprise resource planning system from Vendor X and provides additional business processes that are customized to the needs of Company B.
Figure 6.2 illustrates an architecture for this application. The middle tier is composed of enterprise beans and JSP pages that provide customization of business processes and support a company standardized Web interface. This application enables an employee (under the different roles of Manager, HR manager, and Employee) to perform various personnel management functions: personal information management, payroll management, compensation management, benefits administration, travel management, and cost planning.
The company's IT department deploys this application and enterprise resource planning system in a secure environment at a single physical location. Access to the application is permitted only to employees of the organization based on their roles and access privileges, and within the confines of the organization-wide intranet. 
Company C has a distributed purchasing application whose Web-based interface an employee can use to perform multiple purchasing transactions. An employee can use the application to manage the procurement process, from creating a purchase requisition to getting invoice approval. This application also integrates with the existing financial applications in the enterprise for tracking financial aspects of the procurement business processes.
Figure 6.3 illustrates an architecture for this application. The application as developed and deployed on the J2EE platform is composed of JSP pages, enterprise beans, and existing information systems. The enterprise beans integrate a logistics application that provides integrated purchasing and inventory management functions from Vendor X and another that provides financial accounting functions from Vendor Y.
Company C is a large decentralized enterprise with geographically distributed business units and departments. In this scenario, System X and System Y are managed by different IT departments and have been deployed at secured data centers in different geographic locations. The integrated purchasing application is deployed at a location different from either System X or System Y.
System X and System Y are in different security domains; they use different security technologies and have their own specific security policies and mechanisms. The distributed purchasing application is deployed in a security domain that is different from either that of System X or System Y.
This scenario is an extension of the Internet E-Store scenario described in Section 6.1.1 on page 172 and which the sample application demonstrates as well. Company A has an order fulfillment center that processes all orders placed on the Internet E-Store Web site. A separate department within Company A owns this center. This department maintains its own databases and has no access to the databases of the Internet E-Store Web site. To decouple the data models of the two departments, the order processing center requires that all orders sent to it are in XML format. Since an order might require significant processing, the order processing center receives orders asynchronously so that its clients can continue operation without waiting for an order to be fulfilled.
By using automated rules for small orders, the order processing center can process such orders without human intervention. All other orders require approval by an administrator. When an order is successfully completed, the center sends a confirmation e-mail to its customer. The administrator can also receive various kinds of sales data, such as daily sales volume, sales per category, and so forth.