Preliminary support for monitors.

* src/tgbatest/ltl2tgba.cc (-M): New option for building
deterministic monitors.
* src/tgbaalgos/minimize.cc (minimize): Take a monitor
argument and adjust the code.
* src/tgbaalgos/minimize.hh (minimize): Document it.

ChangeLog

@@ -1,3 +1,13 @@
+2010-11-25  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
+
+	Preliminary support for monitors.
+
+	* src/tgbatest/ltl2tgba.cc (-M): New option for building
+	deterministic monitors.
+	* src/tgbaalgos/minimize.cc (minimize): Take a monitor
+	argument and adjust the code.
+	* src/tgbaalgos/minimize.hh (minimize): Document it.
+
 2010-11-25  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
 
 	"ltl2tgba -Rm -X foo.tgba" would fail.

src/tgbaalgos/minimize.cc

@@ -135,14 +135,14 @@ namespace spot
     return res;
   }
 
-  tgba_explicit* minimize(const tgba* a)
+  tgba_explicit* minimize(const tgba* a, bool monitor)
   {
     // The list of accepting states of a.
     std::list<const state*> acc_list;
     std::queue<hash_set*> todo;
     // The list of equivalent states.
     std::list<hash_set*> done;
-    tgba_explicit* det_a = tgba_powerset(a, &acc_list);
+    tgba_explicit* det_a = tgba_powerset(a, monitor ? 0 : &acc_list);
     hash_set* final = new hash_set;
     hash_set* non_final = new hash_set;
     hash_map state_set_map;

src/tgbaalgos/minimize.hh

@@ -1,4 +1,4 @@
-// Copyright (C) 2009, 2010 Laboratoire de Recherche et Développement
+// Copyright (C) 2009, 2010 Laboratoire de Recherche et Développement
 // de l'Epita (LRDE).
 //
 // This file is part of Spot, a model checking library.
@@ -25,8 +25,74 @@
 
 namespace spot
 {
-  tgba_explicit* minimize(const tgba* a);
+  // \brief Use the powerset construction to minimize a TGBA.
+  //
+  // If \a monitor is set of \c false (the default), then the
+  // minimized automaton is correct only for properties that belong to
+  // the class of "obligation properties".  This algorithm assumes
+  // that the given automaton expresses an obligation properties and
+  // will return an automaton that is bogus (i.e. not equivalent to
+  // the original) if that is not the case.
+  //
+  // Please see the following paper for a discussion of this
+  // technique.
+  //
+  // \verbatim
+  // @InProceedings{	  dax.07.atva,
+  //   author	= {Christian Dax and Jochen Eisinger and Felix Klaedtke},
+  //   title		= {Mechanizing the Powerset Construction for Restricted
+  // 		  Classes of {$\omega$}-Automata},
+  //   year		= 2007,
+  //   series	= {Lecture Notes in Computer Science},
+  //   publisher	= {Springer-Verlag},
+  //   volume	= 4762,
+  //   booktitle	= {Proceedings of the 5th International Symposium on
+  // 		  Automated Technology for Verification and Analysis
+  // 		  (ATVA'07)},
+  //   editor	= {Kedar S. Namjoshi and Tomohiro Yoneda and Teruo Higashino
+  // 		  and Yoshio Okamura},
+  //   month		= oct
+  // }
+  // \endverbatim
+  //
+  // Dax et al. suggest one way to check whether a property
+  // \f$\varphi\f$ expressed as an LTL formula is an obligation:
+  // translate the formula and its negation as two automata \f$A_f\f$
+  // and \f$A_{\lnot f}\f$, then minimize both automata and check that
+  // the two products $\f \mathrm{minimize(A_{\lnot f})\otimes A_f\f$
+  // and $\f \mathrm{minimize(A_f)\otimes A_{\lnot f}\f$ are empty.
+  // If that is the case, then the minimization was correct.
+  //
+  // You may also want to check if \$A_f\$ is a safety automaton using
+  // the is_safety_automaton() function.  Since safety properties are
+  // a subclass of obligation properties, you can apply the
+  // minimization without further test.  Note however that this is
+  // only a sufficient condition.
+  //
+  // If \a monitor is set to \c true, the automaton will be converted
+  // into minimal deterministic monitor.  All useless SCCs should have
+  // been previously removed (using scc_filter() for instance).  Then
+  // the automaton will be reduced as if all states where accepting
+  // states.
+  //
+  // For more detail about monitors, see the following paper:
+  // \verbatim
+  // @InProceedings{	  tabakov.10.rv,
+  //   author	= {Deian Tabakov and Moshe Y. Vardi},
+  //   title		= {Optimized Temporal Monitors for SystemC{$^*$}},
+  //   booktitle	= {Proceedings of the 10th International Conferance on
+  // 		  Runtime Verification},
+  //   pages		= {436--451},
+  //   year		= 2010,
+  //   volume	= {6418},
+  //   series	= {Lecture Notes in Computer Science},
+  //   month		= nov,
+  //   publisher	= {Spring-Verlag}
+  // }
+  // \endverbatim
+  // (Note: although the above paper uses Spot, this function did not
+  // exist at that time.)
+  tgba_explicit* minimize(const tgba* a, bool monitor = false);
 }
 
-
 #endif /* !SPOT_TGBAALGOS_MINIMIZE_HH */

src/tgbatest/ltl2tgba.cc

@@ -213,6 +213,11 @@ syntax(char* prog)
             << "  -Rm   attempt to minimize the automata" << std::endl
 	    << std::endl
 
+            << "Automaton conversion:"
+            << "  -M    convert into a deterministic minimal monitor "
+	    << "(implies -R3 or R3b)" << std::endl
+	    << std::endl
+
 	    << "Options for performing emptiness checks:" << std::endl
 	    << "  -e[ALGO]  run emptiness check, expect and compute an "
 	    << "accepting run" << std::endl
@@ -316,6 +321,7 @@ main(int argc, char** argv)
   bool graph_run_tgba_opt = false;
   bool opt_reduce = false;
   bool opt_minimize = false;
+  bool opt_monitor = false;
   bool containment = false;
   bool show_fc = false;
   bool spin_comments = false;
@@ -632,6 +638,10 @@ main(int argc, char** argv)
         {
           opt_minimize = true;
         }
+      else if (!strcmp(argv[formula_index], "-M"))
+        {
+          opt_monitor = true;
+        }
       else if (!strcmp(argv[formula_index], "-s"))
 	{
 	  dupexp = DFS;
@@ -856,6 +866,14 @@ main(int argc, char** argv)
 	  to_free = a;
 	}
 
+      if (opt_monitor && ((reduc_aut & spot::Reduce_Scc) == 0))
+	{
+	  if (dynamic_cast<spot::tgba_bdd_concrete*>(a))
+	    symbolic_scc_pruning = true;
+	  else
+	    reduc_aut |= spot::Reduce_Scc;
+	}
+
       if (symbolic_scc_pruning)
         {
 	  spot::tgba_bdd_concrete* bc =
@@ -976,6 +994,13 @@ main(int argc, char** argv)
 	  tm.stop("WDBA-check");
 	}
 
+      if (opt_monitor)
+	{
+	  tm.start("Monitor minimization");
+	  a = minimized = minimize(a, true);
+	  tm.stop("Monitor minimization");
+	}
+
       spot::tgba_reduc* aut_red = 0;
       if (reduc_aut != spot::Reduce_None)
 	{