How can one processmap can call another processmap using process API?

Problem description : if we create two process maps P1 (with steps: Step1, Step2 and Step3) and P2 (with Step5). There are two separate process maps and not sub-maps. Call P2 process map from Step1 of P1 using process service API. Is that possible and if yes what happens to P1 at the time of calling P2. And when P2 is completed what happens to P1 then.
Answer: There is no need to use process API for the same. One can leverage workflow Create function from the process map itself for launching P2. They will be 2 independent processes but if you want to establish a link between these 2 processes then put P1 on WaitForCondition till completion of P2.