Windows Workflow Foundation and Application Communication
Windows Workflow Foundation (WF) supports local communication services in a workflow's hosting environment and Web service communications. For information about Web service communications, see Communicating with Other Workflows
WF communication services enable a workflow to interact with an external system through messaging with events and methods. Events are used for sending data to a workflow, whereas methods are used by the workflows to send data to the host application. The ability to communicate with workflows through events provides an asynchronous way to send data to a workflow.