IBM BPM, V8.0.1, All platforms > Authoring services in Integration Designer > Services and service-related functions > Building mediation flows > Aggregating and broadcasting messages

Example: Fan Out and Fan In

This example shows how elements in an array of business objects are updated with the result of a service invocation response. This is achieved by using the Fan Out, Service Invoke, Mapping (using XSL Transformation) and Fan In primitives.

The payload of the input message into the mediation flow consists of an array, MyBoArray, which contains a list of MyBo business objects. MyBo has two fields:

The service request that is input into the mediation flow contains data for field1. This data is passed to another service that populates field2 with data based on the value of field1. This is done iteratively for all data elements in the array, and the result is returned back to the service requester.

Lets assume that there are two data elements (myBOs) in the array that is input into the mediation flow, as shown in the xml below: 

<?xml version="1.0" encoding="UTF-8"?>
<ns0:inputArray xmlns:ns0="http://TestLib/ArrayInterface" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <myBos>
    <field1>049</field1>
    <field2></field2>
  </myBos>
  <myBos>
    <field1>077</field1>
    <field2></field2>
  </myBos>
</ns0:inputArray>

These are the steps in the mediation flow:


Procedure

  1. The user sets MyBoArray to be the shared context in the properties page of the input node.

  2. The user sets the Fan Out primitive to fire the output operation for each element in the XPath expression /body/operation1/inputArray/myBos. The Fan Out primitive performs the following actions:

    1. Populates the iteration count in the Fan Out primitive context with the element count of 2.
    2. Copies the first array element from the message body to the Fan Out context
    3. Fires the output terminal with the Fan Out context containing the first element, which has 049 as the value of field1

  3. The interface of the service invoked by the service invoke primitive takes a business object, MyBo as input. In XSLT1, the user defines a map between the element from the Fan Out context to the elements of MyBo in the input message body.

  4. Service Invoke calls out to the service and puts the response in the output message body.

  5. In XSLT2, the user defines a mapping between the response from the output message body and the shared context business object that was set in step 1.

  6. The Fan in primitive is the decision point in the flow. Because the count of two has not been reached, the mediation flow tracks back to FanOut1.

    1. FanOut1 copies the second array element from the message body to the Fan Out context
    2. Fires the output terminal with the Fan Out context containing the second element, which has 077 as the value of field1
    3. Steps 3 - 6 are repeated. All the elements in the array are now populated with data in the shared context.
    4. Because the count of two has been reached, Fan In fires its output terminal.

  7. In XSLT3, the user defines a map between the elements of the shared context business object to the input message body.

Aggregating and broadcasting messages