Use Process References

In Service Studio you can use processes that are exposed by another eSpace, called, in this context, a Producer. Simply add these processes as eSpace references (Is an element exposed by a Producer eSpace or extension that, when referenced by a Consumer eSpace, is called an eSpace reference in its context. Once an eSpace reference, e.g. an action or entity, is added, you can use it anywhere in the Consumer eSpace but you cannot change its definition.) of your eSpace, called, in this context, a Consumer eSpace.

How to Add a Process Reference:

In the Consumer eSpace, launch the Add/Remove References window, select the Producer eSpace in this window and then check the process that you want.

Once processes are added as references, you can use them in your eSpace:

In any process flow (Collection of elements that graphically implement the behavior of a process. You can have flow control elements (Start, Decision, ..., End), activity elements, and you can invoke other processes. Elements in an process flow are linked through Connectors.), by dragging the Execute Process tool from the Tools tree, into the flow, and choosing the referenced process in the Process property. A quicker way to do this is simply dragging the referenced process from the eSpace Tree into the flow.
In any action flow (Collection of elements that graphically implements the behavior of an action. You can have assign and control elements, exception handlers or you can invoke other actions. The elements are linked through Connectors.), by dragging the Launch<Referenced Process Name> action from the Processes folder of the Tools tree, into the flow, just like any other action.

Process references are executed in a manner that is most similar to the way action references are executed. See how.