34 Using IBM WebSphere Message Broker as an ESB with WebSphere Process Server
3.4.2 Aggregation with message flows
Aggregation is a mediation concept that involves the collection of the responses
from two or more applications to fulfill a request from the requester. The
responses are merged into a single message and sent to the requester or to
another target application.
Aggregation in message flow applications can be described in three phases:
1. A message is received by the message broker. Based on this message, the
broker requests information from one or more applications. The following
examples are of initial message processing:
– The initial message is a request that can be forwarded as a request to
begin the aggregation.
– The initial message requires parsing, so that parts of the message can be
used to build different requests, where each request is sent to the
corresponding application whose response will be aggregated with the
others.
– The initial message might need to be enriched in order to build the
aggregation request.
– The initial message might not have arrived over the MQ transport, so it
needs to be transformed before the request is built.
2. After the message is processed and the requests are built, the requests are
sent to the respective applications. The process of sending the requests is
referred to as the
fan-out process. The fan-out process can involve sending
the request to any application that supports the MQ request-reply interaction
model. Two built-in nodes are supplied for use in the fan-out flow: the
AggregateControl node and the AggregateRequest node.
If an application does not support the MQ request-reply interaction model,
another message flow can be used to act as an interface to the application
whose response is needed for the application. For example, if a Web service
response is needed for the aggregation, an additional message flow can be
introduced to act as an interface between the aggregation message flow
application and the Web service by implementing the Web service with an
MQ interface.
For more information about how to expose a Web service as an MQ
application service, search on “Broker implements non-web-service interface
to new Web service” in the WebSphere Message Broker Information Center:
http://publib.boulder.ibm.com/infocenter/wmbhelp/v6r0m0/index.jsp
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