Service merger Application

The built-in Service merger Application allows to:

• Merge several services in one
• Split one service in several services

Technically, what it does is:

• Setting values for the datas in Services for which the serviceMerger is a provider
• With the values for the datas in Services for which the serviceMerger is a subscriber

The Services for which the serviceMerger is a provider which will be invoked are those which are related to the received datas (if the data valeus have changed).

Application properties

The application configuration has one mandatory property:

• "config": the path of the merge configuration. See Service Merger configuration for how to configure the Module

Example usage of a Service merger

This example shows a use case for the Service merger built-in application.

The misaligned Services problem

Suppose we have the following architecture:

We have two modules:

The aircraft module which uses the aircraft attitude and position:

      <module name="Aircraft" >
         <interfaces>
            <subscribe service="attitude" />
            <subscribe service="position" />
         </interfaces>
      </module>

We have the following services definition:

      <services>
         <publish name="attitude" >
            <data name="theta" type="float" />
            <data name="phi" type="float" />
         </publish>
         <publish name="position">
            <data name="latitude" type="float" />
            <data name="longitude" type="float" />
            <data name="altitude" type="float" />
         </publish>
      </services>

And the SimulationEngine module which computes the aircraft characteristics:

      <module name="SimulationEngine" >
         <interfaces>
            <push service="aircraftModel" />
         </interfaces>
      </module>

We have the following service definition:

      <services>
         <publish name="aircraftModel" >
            <data name="theta" type="float" />
            <data name="phi" type="float" />
            <data name="acLatitude" type="float" />
            <data name="acLongitude" type="float" />
            <data name="acAltitude" type="float" />
         </publish>
      </services>

We would like to compute the aircraft data by the SimulationEngine module and use them by the aircraft module but is is not possible because they use different services even if in fact they use the same datas. it is not in this case possible to use a Service alias because just renaming a Service would not work. One solution is to define another module using the Service merger Application.

Service merger solution

We can define a new Service merger Application with the following architecture:

This module will make the bridge between the aircraftModel Service and the position and attitude Services.

      <mergerConf>
         <outputService name="attitude" >
            <inputService name="aircraftModel" />
            <data name="theta" fromData="theta" fromService="aircraftModel" />
            <data name="phi" fromData="phi" fromService="aircraftModel" />
         </outputService>
         <outputService name="position" >
            <inputService name="aircraftModel" />
            <data name="latitude" fromData="acLatitude" fromService="aircraftModel" />
            <data name="longitude" fromData="acLongitude" fromService="aircraftModel" />
            <data name="altitude" fromData="acAltitude" fromService="aircraftModel" />
         </outputService>
      </mergerConf>