IBM SG24-6526-00 Messaging Java Message Service and IBM WebSphere MQ, call.connect, contract

For vendor.connect, Figure 2-2shows the relationship between the controlling servlet and the vendor.connect subsystems.

		supplier
	contract
Generic	shipment	fulfillment
Servlet
	purchaseorder

Figure 2-2 vendor.connect dependencies

call.connect components are designed to be extensible, reusable, and replaceable. This means that the business functionality can be extended without needing to cut and paste entire programs. This helps to reduce maintenance overhead and allows existing code to be reused.

2.2 Messaging: Java Message Service and IBM WebSphere MQ

The term messaging refers to the sending of structured information between two or more subsystems. Typically the message is sent asynchronously. That is that the sender can continue to run without waiting for a reply from the receiver. Also, the sender and receiver typically run as separate processes and possibly on physically separate machines.

2.2.1 call.connect

Both call.connect and vendor.connect use asynchronous messaging to meet specific requirements:

call.connect uses messaging to meet two requirements:

￿To send information back to the client user interface (UI) such as “the order has been put on hold due to credit problems”, or “a given item is out of stock”

￿To allow for time-consuming steps to be completed asynchronously, for example, order completion when the order is actually committed into System21

12Geac System21 commerce.connect: Implementation on the iSeries Server