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+.. This work is licensed under a Creative Commons Attribution 4.0 International License.
+.. http://creativecommons.org/licenses/by/4.0
+.. Copyright 2017 Huawei Technologies Co., Ltd.
+
+BPMN Main Process Flows
+========================
+
+Characteristics
+----------------
+
+**Invoked by an API Handler**
+
+  The BPMN application (war) exposes a REST endpoint to which the API Handler(s) send requests for flow execution.  The message sent by the API Handler to this endpoint is a JSON wrapper containing:
+  
+    * The original request received by the API handler from the portal or other client.
+    * Metadata such as the request-id generated by the API Handler for the request.
+    * The name of the BPMN process to execute (obtained by the API Handler from the mso_catalog.service_recipe table.
+  
+**Asynchronous Service Model**
+  
+  All main process flows implement an asynchronous service model.  The connection to the API Handler is kept open until the main process flow sends back a response.  In the flow shown below, this is done by the "Send Sync Ack Response" script task.  A flow is expected to send a response after validating the request, but before performing any long running tasks or tasks that could cause the process to be suspended.
+  
+  After the synchronous response is sent, the flow continues to execute.  When the flow ends, it may optionally send an asynchronous notification to a callback URL provided in the original request (behavior depends on the API agreement)
+  
+**Typically calls one or more subprocess flows**
+
+  Main process flows usually implement the high-level service logic, delegating the "real" work to reusable subflows (Building Blocks) or custom subflows
+  
+**Handles "Completion" and "Fallout" tasks**
+
+  "Completion" tasks are those that occur when the process ends successfully, and "Fallout" tasks are those that occur when the process fails.  Activities include:
+  
+    * Updating the mso_requests database.
+    * Rolling back uncompleted work.
+    * Sending an asynchronous callback notification.
+
+Example: CreateVfModuleVolumeInfraV1.bpmn
+------------------------------------------
+
+.. image:: images/BPMN_Main_Process_Flows_1.png
+\ No newline at end of file