# Dynamic Controllability of Processes without Surprises
###### Abstract  
Dynamic controllability guarantees that a process control can steer the execution of a business process without violating any temporal constraints although some tasks have uncontrollable durations. However, it has been shown that dynamic controllability may lead to process executions with the undesirable property that tasks have to be started or ended on extremely short notice. Sudden termination forces the agent to immediately terminate the execution of a process task without any prior notice in order to meet some temporal constraints. Semi-dynamic controllability guarantees dynamic controllability and the absence of sudden termination. Here, we show that dynamic controllability may also lead to the problem of sudden start, which forces the immediate start of a process task without prior notice. We formalize all constellations of temporal constraints causing sudden start and sudden termination in a process. We propose a technique to design processes in which activities can be dynamically dispatched without these surprises, i.e., with advance notice, and extend the notion of semi-dynamic controllability by also considering the sudden start. This leads to a sound and complete algorithm for checking the semi-dynamic controllability of time-constrained processes. process scheduling; contingent durations; sudden start; sudden termination; dynamic controllability +
Footnote †: journal: Applied  
causes of uncertain durations are the invocation of external services or the dependencies on other controllers in cross-organizational processes (see e.g., [8]) where service level agreements provide duration intervals. For processes with contingent activities, _dynamic controllability_[6; 7] is the notion for temporal correctness that is preferred to, e.g., the satisfiability of temporal constraints. Satisfiability requires the existence of one possible instance of a process that satisfies all temporal constraints. On the contrary, dynamic controllability requires that there exists a dynamic execution strategy for the process controller to set the start and end of activities in response to all possible durations of contingent activities revealed at run time. We refer to [9; 10] as examples of techniques that can be adopted to efficiently check dynamic controllability of processes. Despite being a much desirable property for a time-constrained process, dynamic controllability can present an undesirable side effect. Indeed, a dynamically controllable process might admit only dynamic execution strategies that force (1) some activities to start, without knowing yet when they need to finish (_sudden termination_), and (2) some activities to start immediately without prior notice (_sudden start_). We use the term _sudden_ to describe such phenomena since they require, at run time, to schedule the termination, resp. start of a process activity immediately, without giving the executor any time to prepare for such an event. In our prior work [11], we have addressed the sudden termination problem. We characterized _semi-contingent_ activities, which require to set their duration, resp. their deadline, when they start, i.e., their duration can be chosen by the controller, but only until they start. In particular we have shown in detail one sudden termination pattern, and only sketched other patterns that may lead to such a sudden termination. This paper is an extension of the work in [11]. As such, it covers all sudden termination patterns shown in [11] in more detail, and addresses the additional problem of sudden start. So the research question driving this extended paper is: _how to determine whether the start and end events of process tasks can be scheduled with a given advance notice, meeting all temporal constraints, despite uncertainties?_  
Here, we propose a technique to support process designers in checking whether it is possible to steer a process with the guarantee that no sudden (start or end) event needs be dispatched at run time.