Coupling coefficients of a distributed execution

We define coupling coefficients of a distributed execution which evaluate the temporal interactions of a distributed execution between the processes during the execution. These coefficients assess the structure of message exchanges rather than the quantity of exchanged information. The coupling coefficients are easy to compute and provide a criterion to compare and to analyze distributed executions. We check the relevance of our definitions by computing these coefficients for particular cases and by studying their behavior with respect to operators which are defined on the distributed computations. This leads us to establish noteworthy results concerning the behavior of execution times with respect to these operators. Finally, we regard the coupling coefficients as functions of the relative processor speeds and characterize the executions for which coupling is minimal or maximal.