Adapting an AI Planning Heuristic for Directed Model Checking

Downward pattern refinement for timed automata

“…Second, on a practical level for timed automata, although there are several distance heuristics "on the market" (as discussed in the introduction), many of these distance heuristics are not able to properly deal with clock variables. In more detail, there are powerful distance heuristics that have been proposed for timed automata that just ignore the clock variables, and focus on the automata and integer variables instead [9,22]. However, considering the definition of relatively accurate abstractions, we observe that if the applied distance heuristic does ignore clocks, then abstracting all clocks will always lead to relatively accurate abstractions.…”

“…2, and assume that we want to abstract a, i.e., P = {P, Q, x}. Further assume that we want to check if S| P is the relatively accurate abstraction of S induced by the h L heuristic [22] and P. The h L heuristic relaxes the concrete system semantics by assuming that discrete variables become set-valued, and all values obtained during the computation of a trace are unified to this set. Constraints are evaluated to true if there exist corresponding values in these sets.…”

“…The most related approach to this work is probably the "Russian Doll" abstraction that has been proposed by Kupferschmid et al [23]. In this approach, the pattern selection problem is addressed by computing an abstract error trace π using the so-called monotonicity abstraction [22], and then collecting all variables that occur in π for the pattern. The underlying idea is that variables that occur in the abstract error trace π are likely to be important for the abstract system as well.…”

“…One of these approaches is based on the above-mentioned monotonicity abstraction proposed for directed model checking by Kupferschmid et al [22]. First, let us remark that despite the name, the monotonicity abstraction is not an abstraction in the sense we described so far, but rather a relaxation of the original system semantics with the following underlying idea: System variables keep track of the values achieved so far, and transitions are applicable if there is a combination of so far achieved values such that the guards are satisfied.…”

“…Directed model checking has recently found much attention in different variants and contexts [9,12,14,19,22,23,30,32,[34][35][36][37]. For a given model M of a system, the main idea is to focus the search on those parts of the state space of M that appear to be promising to contain a reachable error state.…”