O'Reilly - Java Message Service

1.3.1 Enterprise Application Integration
Java Message Service
Most mature organizations have both legacy and new applications that are implemented
independently and cannot interoperate. In many cases, organizations have a strong desire
to integrate these applications so they can share information and cooperate in larger
enterprise-wide operations. The integration of these applications is generally called
Enterprise Application Integration (EAI).
A variety of vendor and home-grown solutions are used for EAI, but enterprise messaging
systems are central to most of them. Enterprise messaging systems allow stovepipe
applications to communicate events and to exchange data while remaining physically
independent. Data and events can be exchanged in the form of messages via topics or
queues, which provide an abstraction that decouples participating applications.
As an example, a messaging system might be used to integrate an Internet order processing
system with an Enterprise Resource Planning (ERP) system like SAP. The Internet system
uses JMS to deliver business data about new orders to a topic. An ERP gateway
application, which accesses a SAP application via its native API, can subscribe to the order
topic. As new orders are broadcast to the topic, the gateway receives the orders and enters
them into the SAP application.
1.3.2 Business-to-Business
Historically, businesses exchanged data using Electronic Data Interchange (EDI) systems.
Data was exchanged using rigid, fixed formats over proprietary Value-Added Networks
(VANs). Cost of entry was high and data was usually exchanged in batch processes - not
as real-time business events.
The Internet, XML, and modern messaging systems have radically changed how
businesses exchange data and interact in what is now called Business-to-Business (B2B).
The use of messaging systems is central to modern B2B solutions because it allows
organizations to cooperate without requiring them to tightly integrate their business
systems. In addition, it lowers the barriers to entry since finer-grained participation is
possible. Businesses can join in B2B and disengage depending on the queues and topics
with which they interact.
A manufacturer, for example, can set up a topic for broadcasting requests for bids on raw
materials. Suppliers can subscribe to the topic and respond by producing messages back to
the manufacturer's queue. Suppliers can be added and removed at will, and new topics and
queues for different types of inventory and raw materials can be used to partition the
systems appropriately.
1.3.3 Geographic Dispersion
These days many companies are geographically dispersed. Brick-and-mortar, click-andmortar,
and dot-coms all face problems associated with geographic dispersion of enterprise
systems. Inventory systems in remote warehouses need to communicate with centralized
back-office ERP systems at corporate headquarters. Sensitive employee data that is
administered locally at each subsidiary needs to be synchronized with the main office.
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