Architecting and designing : DoDAF : DoDAF 1.5 Activity Based Methodology (ABM) : Developing operational views with DoDAF ABM : ABM syntax rules : OV-5 leaf activities must have at least one input and one output
  
OV-5 leaf activities must have at least one input and one output
To form Information Exchanges at the leaf activities, they must have at least one input from either another activity or an external activity and at least one output to another activity or an external activity.
In the following examples, the second diagram fixes the invalid syntax with an input.
Valid input drawn:
See also
ABM syntax rules