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When used for integration, an enterprise very likely requires that all partici 

pating EIS systems communicate with each other by sending messages via the

messaging system. As a result, enterprises typically standardize on one vendor for

their MOM system, and they use that vendor's adapters to accommodate their

various EISs. In return, enterprises using messaging systems gain the benefits of

asynchronous messaging calls: Messages are queued and delivered when the

target system is available without constraining the sending system. The asynchro 

nicity of messaging systems means that communicating applications need not be

currently running to receive messages. This protects the communicating applica 

tions from system failures and other types of partial outages, conditions that are

not uncommon in network situations.

Messaging systems also bring a dynamic quality to EIS systems. Components

can be added or removed to the network without affecting other systems. Systems

do not need to have their throughputs perfectly match since they can interact with

the messaging system at their own pace. For example, if one application sends

messages more rapidly than the receiving application can retrieve these messages,

the messaging system keeps these messages in the queue indefinitely. As a result,

good overall throughput is achieved since each part of the system can work at its

optimum capacity.

Furthermore, messaging technology is considered a fairly mature technology.

Most MOM systems provide a number of quality of service features, such as reli 

able once and only once delivery, load balancing, scalability, fault tolerance, and

transactional support. 

However, the proprietary nature of MOM systems results in some significant

disadvantages. Since they use proprietary protocols over the network, it is usually

more difficult to mix and match MOM products from different vendors. Although

messaging systems decouple the sender and receiver and permit communicating

parties to run on different hardware and software platforms, they fall short of

achieving true interoperability because they tie developers to their proprietary

APIs to send and receive messages. As a result, application developers must cus 

tomize their applications for different MOM systems.

6.2.2.2

Java Message Service

The Java Message Service (JMS) API, a standard Java API defined for enterprise

messaging systems, can be used across different types of messaging systems. A Java

application uses the JMS API to connect to an enterprise messaging system. Once

connected, the application uses the facilities of the underlying enterprise messaging