I do not know about the BPMN 1.2 but I can tell you the different ways that a flow can be started"
1. Watched Folder - process monitors a folder on the server and when a new file is created that file is associated with the input of the process and it is started.
2. Email - same as above but email is used with an attachment
3. Java api - programatic interace for java programs
4. Soap Service - programatic interface for any program
5. Data Services end point - used from a flex application
6. Rest call - submission across HTTP/s
Hope that helps
Paul