Parameters to Embedded SAIL

@riccardob, A webapi can do more than just start a process (complete task, write to data store, etc), so it's more flexible than just exposing a process as a web service. The problem with the double webapi approach is that you're not guaranteed that the task you want has been activated by the time the second call goes through. (I've done a hack-y solution that seems to work, but I'm not going to suggest that publicly)
The other approach would be to have Appian "callback" to your Application, and handle that callback on your server side to trigger a reaction to the appropriate client, using something like Server Side Events/websockets. That technology is a bit new, so it will depend on how custom your external app is on whether you could implement something with that.

@riccardob, A webapi can do more than just start a process (complete task, write to data store, etc), so it's more flexible than just exposing a process as a web service. The problem with the double webapi approach is that you're not guaranteed that the task you want has been activated by the time the second call goes through. (I've done a hack-y solution that seems to work, but I'm not going to suggest that publicly)
The other approach would be to have Appian "callback" to your Application, and handle that callback on your server side to trigger a reaction to the appropriate client, using something like Server Side Events/websockets. That technology is a bit new, so it will depend on how custom your external app is on whether you could implement something with that.