Repairing Timed Automata Clock Guards through Abstraction and Testing

Abstract

Timed automata (TAs) are a widely used formalism to specify systems having temporal requirements. However, exactly specifying the system may be difficult, as the user may not know the exact clock constraints triggering state transitions. In this work, we assume the user already specified a TA, and (s)he wants to validate it against an oracle that can be queried for acceptance. Under the assumption that the user only wrote wrong guard transitions (i.e., the structure of the TA is correct), the search space for the correct TA can be represented by a Parametric Timed Automaton (PTA), i.e., a TA in which some constants are parametrized. The paper presents a process that (i) abstracts the initial (faulty) TA \( ta_{init} \) in a PTA \( pta \); (ii) generates some test data (i.e., timed traces) from \( pta \); (iii) assesses the correct evaluation of the traces with the oracle; (iv) uses the IMITATOR tool for synthesizing some constraints \(\varphi \) on the parameters of \( pta \); (v) instantiate from \(\varphi \) a TA \( ta_{rep} \) as final repaired model. Experiments show that the approach is successfully able to partially repair the initial design of the user.