Re: The REST API for a workflow created by graphical interface?
Based on your diagram, the two REST components you have there are basically REST clients. When you start the process, those tasks will invoke the REST APIs you have configured using those components. Basically those two REST components in your process are REST clients. If I understand your question correctly, you want to start the process instance through an REST API. Yes, that is possible. Alfresco Process Service comes with a rich set of APIs. There are APIs that allow you to start a process instance. Please refer the documentation for more details: Start Process Instance | Alfresco Documentation
If you have the latest version installed, you should be able to browse through all the APIs using the API Explorer which is available at http://localhost:8080/activiti-app/api-explorer.html (assuming you have Alfresco Process Service installed on your localhost running on 8080. Otherwise, please modify the url accordingly). You can also use the cloud instances's API Explorer to browse the API documentation which is available at Alfresco Process Services API Explorer