A start is a starting point of the flow represented in the diagram.

A start can be created in a choreography diagram with any of the following target languages:
        In decomposed processes, only one start is allowed per diagram, except for analysis business process diagrams. The Start tool is unavailable if a start symbol already exists. You should not use the same start in two diagrams, and you cannot create shortcuts of starts.
            - 
                    Activity Diagram -  one or more per diagram 
- 
                    Statechart Diagram -  one or more per diagram 
- 
                    Interaction Overview Diagram -  one only per diagram 
 
Note: 
            
The start is compared and merged in the Merge Model feature, which checks that there is no additional start in decomposed processes
                .