Page - 174 - in Intelligent Environments 2019 - Workshop Proceedings of the 15th International Conference on Intelligent Environments

4.1. ObservationofCommunicatingProcesses We consider the following typical situation in the interaction of communicating pro- cesses,where aprocessA, the caller, issues anoperation at theprocessB, the callee. In figure 1, the caller sends amessageM to the callee, which processes themessage and issues the operation accordingly. Finally, the operation returns a resultM′. In this sce- Figure1. Messagebased interaction Figure2. Messagedispatchat callee nario,weassumeaworkingcommunicationandthat thecalleesyntacticallyunderstands themessages. This enables the callee to parse the receivedmessage and dispatch it to theappropriateoperation.Figure2displays the linkbetween themessage receptionand operationvia thedispatcher.Atfirst, thedispatcher identifies theoperationop specified in themessage andmaps it to the appropriate local operation. The operation starts and afterwards the result R=op(M) indicates the end of the operation,whether the opera- tion ran successfully or failed. Rmaybe even empty as long aswe canfigure out that it originates from the callee’s operation op. In case themessage specifies an unknown operation the dispatcher returns some other resultU, which can be distinguished from resultR. Independent fromthecontent, resultRandresultUmustat least identify there- sult’soriginator.Wheneveramessage is receivedby thecallee,oneofRorU is created. A newmessageM′ includes this result and is returned by the callee to inform the the caller. The key observation relevant for interoperabilitymeasurement is that the callee receives amessage and creates a result fromwhich it can be detectedwhether an oper- ationwas issued or not. Again, the concrete result of the operation’s execution aswell as the informationwhether theoperation ran successfullyor failed isnot relevant in this context. 4.2. MessagePassingof InteroperableProcesses Weformulate the observation of themessage passing behavior fromFigure 2 for inter- operableprocesseson theconsolidation levelof theC4IFschemeas follows: Observation (Messagepassing). If an interoperableprocess receivesamessageM, the process’s operation op will cause the process to emit a non-arbitrary outgoing mes- sageM′. Note that we use the term outgoingmessage as an indicator that the operation op was issuedby the incomingmessage. It isnot required that theoutgoingmessage is sent S. Kotstein and C. Decker /AnApproach for Measuring IoT Interoperability174