Chapter 6. EIS integration using Java Message Service 123
6.2 Message-based EIS integration
It has become increasingly important for applications to connect to enterprise
information systems (EIS) because of:
???? The advent of Web-enabled applications, where data from disparate
applications is assembled and presented to Web clients.
???? A trend towards business-to-business communication, where data is
exchanged between applications that are owned by different organizations.
???? A recognition that information in various systems is interrelated and that the
true value of information, processes, and events can be achieved only when
the entire virtual enterprise is seen as a unified whole, instead of islands of
applications. The value achieved through automation and integration of
business processes drives competitive advantage.
In these situations, it is important to reuse existing applications and their data
with no or minimal modification regardless of whether they are legacy systems,
newly developed applications, or vendor packages. Recognizing the importance
of integration, EIS providers and software companies developed connectors to
aid system integration. However, these connectors have proprietary
architectures and implementations which present another challenge to EIS
integration.
For many years, distributed application development faced many challenges in
EIS integrations until the emergence of MOM. MOM reduces the complexity that
is involved in integrating disparate, heterogeneous applications that span
multiple operating systems and networking protocols. MOM achieves this by
encapsulating the details and intricate workings of the various operating systems
and network interfaces from the application developers. By providing API
implementations that extend transparently across diverse platforms and
networks, MOM increases the flexibility of an architecture and enables
applications to exchange messages with other programs without having to know
on which platform or processor the other application resides.
Additional advantages of using MOM include:
???? Robustness to change
Applications on heterogeneous platforms communicate and interoperate
independently through standard MOM interfaces. These interfaces allow
applications to be maintained separately and to be replaced individually.
???? Temporally distributed
With MOM, applications communicate asynchronously where neither the
sender nor the receiver needs to be available at the same time. If the
124 Managing Information Access to an EIS Using J2EE and Services Oriented Architecture
receivers are not available, the MOM queues and forwards the messages
when the receivers become available.
???? Location independence
MOM senders and receivers communicate through virtual destinations known
as queues or topics. Message senders address messages to named queues
or topics, and message receivers specify the topics or queues from which
they want messages. This independence de-couples the senders and
receivers. They do not need to know the network addresses of the entities
with which they are exchanging messages, allowing them to communicate
regardless of their physical location. Thus, you can move applications among
machines without disrupting other components.
???? Load balancing
MOM supports priority and load-balancing by allowing retrieval of messages
off the queue in any order. With this, you can deploy multiple messages
receivers to perform concurrent message receipt and processing, thus
increasing performance throughput.
???? Fault tolerance
In MOM, message queues can be configured to be persistent, providing
guaranteed message delivery. This persistent queue feature increases the
system’s fault tolerance because messages can be processed when the
system recovers from failure.
???? Routing
The ability to route messages within the middleware layer itself makes it
possible for a single sender to deliver a message to multiple recipients and
multiple senders to send messages to a single recipient.
6.2.1 Messaging characteristics for EIS integration
MOM has become a mature technology and is widely used for EIS integration.
Companies have successfully built powerful solutions to integrate their EIS
systems. The main features and services provided by MOM that are important for
EIS integration are:
???? Asynchronous communications
A fundamental concept of MOM is that communication between applications
is intended to be asynchronous. So, when a client application sends out a
message to a receiving application, MOM allows the client application to
handle other tasks without waiting for a response from the receiving
application. This non-blocking asychronous communication mode de-couples
application systems from one another. Thus, a failure in one system does not
have an immediate and debilitating impact on other systems.
Chapter 6. EIS integration using Java Message Service 125
???? Guaranteed message delivery
When network systems are up and running, MOM delivers messages from
the senders to the receivers as part of reliable messaging characteristics.
However, network failure may occur or applications that need to be shut down
because of unpredictable failure or regular system maintenance. In
recognition of these situations, MOM provides guaranteed message delivery
which ensures that the intended message consumers receive messages as
soon as network connections are established and the receiving application
issues a request for sent messages.
???? Transaction support
MOM supports transactions and is also tightly integrated with transaction
services. When transaction services are present, they can participate in a
MOM transaction.
???? One time, in-order delivery
MOM can guarantee that each message is delivered once and only once and
that messages are received in the order that they are sent.
???? Message routing services
These services allow the client application to send the message to their
destination using least-cost routing. The administrator needs to define only
the cost of each route, and MOM automatically calculates the most
economical path for the message. Moreover, this routing is capable of
eliminating single points of failure. Thus, MOM can reroute around network
problems.
???? Notification services
Even though MOM allows messages to be sent asynchronously to free up the
client application, in some instances, the sending application might want to be
notified whether the message was received successfully. So, MOM also
allows the sender to review responses, let another application handle them,
or just completely ignore them. For example, a request-reply mechanism can
be employed by the sender to receive notification from the receiver.
???? Scalability
In a MOM system, system scalability can be addressed relative to anticipated
messages volume and desired processing throughput. However, this
approach only applies to situations where messages can be processed in any
order and not first-in-first-out fashion. So, as the number of message
producers increases, processing capacity can be increased by adding more
message consumers that monitor the message destination. This approach
provides flexibility in operational design to allocate adequate hardware
capacity accordingly to processing needs.
126 Managing Information Access to an EIS Using J2EE and Services Oriented Architecture
6.2.2 Point-to-point integration pattern
In a point-to-point topology, each application has a direct connection to invoke
another application’s services. The applications and EIS systems are enabled to
invoke remote services and to exchange messages by implementing a
messaging adapter. The adapter has to transform the messages to a format that
the receiving applications and systems are able to process. Alternatively, the
adapter can generate a canonical representation of the data that has to be
agreed upon across the participating parties.
A domain with N being the number of applications that has a total of N*(N-1)
connections. Figure 6-1 is an example of a point-to-point topology.
Figure 6-1 Point-to-point topology
As the number of applications increases, the complexity and manageability of the
system also increases. To reduce this complexity, a canonical representation of
message formats can be used, or an intermediary server such a broker or a hub
can be introduced to produce a hub-and-spoke topology.
6.2.3 Hub-and-spoke integration pattern
The hub-and-spoke topology introduces an intermediary or broker. The role of
the broker is to reduce the connectivity complexity by having each endpoint
connect to a single entity rather than the other N-1 end points and also to
centralize any integration logic such as transformation, mapping, and routing.
SAP
Legacy
Application
IMS
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