A TGA-based Method for Safety Critical Plan Execution

Safety critical planning and execution is a crucial issue in autonomous systems. This paper proposes a methodology for controller synthesis suitable for timeline-based planning and demonstrates its effectiveness in a space domain where robustness of execution is a crucial property. The proposed approach uses Timed Game Automata (TGA) for formal modeling and the UPPAAL-TIGA model checker for controllers synthesis. An experimental evaluation is performed using a real-world control system

On the Complexity of Temporal Controllabilities for Workflow Schemata

Recently, different kinds of "controllability" have been proposed for workflow schemata modeling real world processes made of tasks and coordination activities. Temporal controllability is the capability of executing a workflow for all possible durations of all tasks satisfying all temporal constraints. Three different types of controllability are possible -- strong controllability, history-dependent controllability, and weak controllability -- and a general exponential-time algorithm to determine the kind of controllability has been proposed. In this paper we analyze the computational complexity of the temporal controllability problem to verify the quality of proposed algorithms. We show that the weak controllability problem is \coNP-complete, while strong controllability problem is in \u3a3_2^P and it is coNP-hard. Regarding the history-dependent controllability problem, we are able to show that it is a PSPACE problem but further research is required to determine its hardness characterization

A Fast Incremental Algorithm for Managing the Execution of Dynamically Controllable Temporal Networks

(STNU) is a network of time points and temporal constraints in which the durations of certain temporal intervals—the contingent links—are bounded, but not controllable. An STNU is dynamically controllable if there is a real-time strategy for executing its non-contingent time points that guarantees the consistency of the network no matter how the durations of the contingent links turn out. Morris presented an O(N 4)-time algorithm for determining the dynamic controllability of arbitrary STNUs, where N is the number of time points. Morris suggested that additional O(N 4)-time computation might be needed to prepare a dynamically controllable network for execution, with all computations done in advance of execution. Instead, this paper shows that an STNU that has passed Morris ’ algorithm is already prepared for execution. The paper presents an incremental, real-time execution algorithm that is guaranteed to successfully execute the time points in a dynamically controllable STNU using O(N 2) space and O(N 4) time. The O(N 4)-time computations are not done in advance of execution, but instead are spread out over the entire time that time points in the network are being executed: N iterations of O(N 3) per iteration. Furthermore, the most costly computations—O(N 3) per iteration—are done while waiting for the next execution event to occur, whereas the time-critical computations require only O(N 2) per iteration