Arrow-segment labels are prescriptive, constraining the meaning of their segment to apply exclusively to the particular data or objects that the arrow segment graphically represents. Arrow meanings are further expressed through fork and join syntax. The side of the box with which an arrow interfaces reflects the arrow's role. Arrows entering the left side of the box are inputs. Inputs are transformed or consumed by the function to produce outputs.
Arrows entering the box on the top are controls.
Controls specify the conditions required for the function to produce correct outputs. Arrows leaving a box on the right side are outputs. Outputs are the data or objects produced by the function. Arrows connected to the bottom side of the box represent mechanisms. Upward pointing arrows identify some of the means that support the execution of the function.